Why can't I just buy a game from Steam, blow through it in a day or two, then bitch vehemently so I can get my money back?
Is that what you're asking?
Lol, jk OP, but... yeah that's why. Sure taking away your key/download, and somehow making sure you didn't possibly, in any way, shape or form store the data so you could pirate a copy..... might work but.... it's also the fact that developers sell games, they don't rent them. I would recommend Gamefly if you want to try games before purchasing them, or do what I do and let it release, read all the reviews on the bigger sites and go form there. That's exactly why I am not interested in Brink: All I have read about it is crap.