Nah, this is a very very bad idea. You would give crackers a really easy time. All they would have to do is buy the game and they would be able to download it and put it on their own servers for everyone to download for free.
Also, what if I download the game, and I have to reformat my harddrive, do I have to buy the game again? You might say that the company could give me an account name and password so that I can download the game any time, but what is to keep pirates from spreading around that name and password?
Also, I like many people I know, prefer to have a nice box and manual, simply because it looks nice. Suppose a game would be download only, it would mean I wouldn't be able to get a nice box!
No, I don't really want this to ever happen.
Tovi 
