For most of the time, people have been buying games the same way: going to a store and buying the game from the box. What happens if you lose the CD or the CD-Key? Most of the times, you lost the game and the only way for getting the game back is buying the game again. There are 2 other options though. Blizzard, in example, offers a simple method for playing their games if you lose the CD by any reason. For World of Warcraft, you can always download the game and then you enter your account info and you'll play again on your account, without losing anything. For Warcraft III, you go to an website and enter your CD-Key and you'll then download the game and play again.
However, lately stores like Steam and even App Store are changing the way people buy games. Those stores allow you to download the game and if you delete the installer, you'll just enter your account again, which is something most companies don''t allow you to do.
This 'advantages' really helps the companies. Imagine the money they waste by distributing the game, making the CDs, the boxes, the manuals and everything. Recently, Ubisoft announced that would stop making the manuals and putting them inside the games. They claim that it would help saving trees (which is actually true), but since they won't reduce price, the only ones who lose are the gamers.
I don't know about most people, but I've always loved to check the manual of the game before playing. It's part of the whole gaming experience. You buy the game, and when you're doing the unboxing, you get the manual and check it out. It's also very useful to read the manual whenever you have a doubt during the game. I don't know the way they'll do it but if you have to leave the game to read the manual it'll really ruin part of the game.
Imagine if you buy a console and the box is arranged the most simple way possible, and it only contains the console, cables and controller. It'll feel like something is missing. And that'd be the manual, tips, safety warnings. Most of it isn't useful, but it is part of the experience. It's hard to describe it, but it's easy to imagine. You buy your brand new PS3 and it comes without manual. Or you buy your brand new top-of-the-line notebook and it doesn't come with that bunch of useless CDs of drivers and stuff. It'll feel like something is missing.
I hope that Ubisoft will find a way to make the in-game manuals easy to use and that they will at least make up for it. Reducing the price of their games is something that most people should find very attractive.