They're based on the way that most Americans travel long distances: you book your flight a month or more in advance, you get a rental car so that you can get around, and you book a hotel room based on how plan on staying.
Since that's how they travel, they tend to assume that over the course of 19 months and seven continents, I was continuously doing all of these things. Nope. I had a handful of flights over the course of the trip-- not many more than most college students do if they fly home for school breaks. I might have reserved myself a hotel room twice. I'm not even certain of that. I never rented a car.
When you think about it, it's a little absurd to think that the flight-rental car-hotel reservation method is so predominant that nobody seems to know another way to travel. I'll admit that routine probably affords the most creature comforts for those who have the money, but it's also probably the most expensive, restrictive, and stressful way you can plan a trip. Even if I'd had the millions of dollars required to do my trip around the world that way, I doubt I would have ever done it.
I think a lot of the strength of this travel regime is that it gives the illusion of security. You'll be guaranteed a way in and back home, at good place to sleep, and a way to get from one to the other. So long as your flight isn't delayed/canceled, your hotel is as advertised, and you can spring for all the little surprise fees etc at the rental car counter.
But I think the other real strength this idea has is that it's all these people know. So here is an incomplete list of alternatives. I'm not saying you have to do things one way or another, but I think more people would travel if they knew more about cheaper and more rewarding things they can use:
Instead of buying tickets months in advance, dealing with airport security, baggage restrictions etc of flying try:
Train. In many countries, this is THE way to travel. In Europe and Japan it's often about the same price as flying, but elsewhere it's a bargain and you can buy your ticket the day of travel without any price repercussions. In some places it even rewards you for buying at the last minute (Trans-Siberian rail, anyone?) You see more of your destination, you can stretch your legs and walk around without fear of turbulence, and you'll meet tons of people. Maybe it's just me, but I almost always end up getting free food from fellow passengers, too. Just bring some snacks to share in return. Check seat61.com for good train resources.
Bus. This is how the rest of the world travels by default. You can buy your ticket five minutes before boarding. In developed countries, if you do it in advance, you can pay as little as US$1 for your fare. It's slow, and a bit more restrictive than train travel in that you can't walk around, but if you're someone who can sleep in a car during road trips, bus may be just the method for you. And in the US, forget the stupid urban myths you've heard about Greyhound-- Bolt bus, Megabus, and Go Bus are just a few of the cheap, reliable companies that are very safe and free of the whatever weird characters you're so scared of.
Boat. These are slower than you probably think they are, but boats are looking for passengers and often crews, and they don't always expect the crew to be experienced. Make sure you meet the captain and other crew first (remember to always ask for permission to board before boarding a boat, it's considered rude to hop on without doing so first) and think hard about whether these are people you want to spend all day, every day with for the length of the voyage. Look at findacrew.com and even Craigslist listings for crew.
Rideshare. Check websites to find someone on a road trip who needs company and some extra money for gas. Multiple websites exist for this but I'm not yet aware of a comprehensive global site. Carpooling.com is probably the closest, though it is quite Europe-centric.
Now instead of the hassle, fees, insurance and licensing headaches of renting a car, try...
Public Transit. It is much more widespread than you think. Even if it's just a rowboat or a van that comes by every day with some dude sticking out the window yelling their destination, you can find public transit anywhere. You might think it's slower, but it's actually often faster than fighting traffic, finding directions, and trying to figure out traffic laws that a local bus driver grew up knowing. Like which side of the road to drive on. It's also a lot cheaper.
Bicycle. This depends a lot on local traffic and weather, but a bike rental is a quick, cheap and easy way to get around most places. Insist on a helmet and lock with your bike, no matter how crazy the locals think you are for doing so.
Walking. You'll see more, you'll get more exercise, and you'll open yourself up to a lot more opportunities than you ever could inside of your rental car by virtue of meeting people and smelling/hearing interesting things and following them. You'll remember more than you would have otherwise as well. Once you get used to it, you'll be amazed how fast and far you can go by foot.
Finally, instead of booking a hotel room, locking yourself into solitude and constrained dates, try...
Connections. Tell everyone about your trip. Someone will almost certainly know someone else who can either put you up or knows someone else who can. One of my most enjoyable stays anywhere was in Hong Kong, where I spent a week with my mother's second-cousin's ex-girlfriend's sister and brother in law. Don't ask outright for a place to stay, but do not be ashamed to say you'd like to meet people. Most people will invite you by reflex alone, if they possibly can. And bring a gift or take them out for a drink/meal sometime. You'll get a free place to stay, and some orientation to your destination by locals.
Hostels. Contrary to popular opinion, in the vast majority of cases hostels are clean, you can get a private room, you can stay all day, you don't have to be a member of any organization, and you don't have to be a certain age to stay there. You will meet far more travelers than you ever would in a hotel. Most travelers you meet will be really interesting people from all over the world. You'll almost always have access to a kitchen and several dozen strangers who would love to cook with you. Plus there are discount activities, tours, and guides available to the destination. I often find that most hostels are better located than most hotels, especially if you like seeing places on foot. Check Hostelling International, hostelbookers.com, and hostelworld.com.
Couchsurfing.org. This website is revolutionizing budget travel. It's only been around for a few years, but it's already at more than 2 million members scattered across virtually every country in the world, and it's growing daily by the thousands. The idea is simple, you make a profile, you get other members who trust you to write you a reference or two (which appears on your public profile and that you cannot edit), and you can then search for other people who live in your destination who have done the same. If you like their profile and they have been endorsed by enough people to make you feel comfortable, you can ask if you can crash on their couch/spare bed/floor. If they like your profile and see you come with good references, they can accept. The result? A free place to stay, and a local host to guide you around. Make sure you bring a gift or buy them a meal/drink. That's actually only the beginning-- there are international meetups, parties, road trips, and a lot more all based on this growing online community of travelers. Once again, it's all at couchsurfing.org.
Apartment Swap Craigslist and other sites are good places to look for apartment swap opportunities if you have a pad you'd like to exchange for someone else's for a week or so. Search for apartment swap and your city of choice, or if you're feeling gutsy, just search for the the city you live in, and see who wants to come to you, and where they can give you a place in exchange.
All these and more can be found in any good guidebook on your destination. I have the most experience with the budget end of things, including Let's Go, Lonely Planet's Shoestring series, and Rough guides. If you have a slightly higher budget, I can also recommend Rick Steve's guides.