This seems like a great idea to me. They could easily do something like use last year's playoffs as an extended demo for the next NBA game they make. At $15-20 having half the teams in the league to choose from is a fairly decent deal. They could do other stuff like that, too. They could even go a step further, and make a NFS like this that has completely unique tracks from the main release which upon loading up the full version acts like a regular track pack DLC.

This isn't a bad idea, your impressions are just tainted by their previous failures on the matter. They can execute this right and make it a very tempting offer. Heck, if they're thinking this through they might even try a program where you get another extended demo if you buy the full version of the game (and submit to having your DLC turned off, to protect from people who try to rent/borrow/trade their way into a bunch of free games).

If they want to charge for a demo, they should charge just enough to cover distribution costs. I mean, I wouldn't mind paying $1 for a DVD with a demo on it. Any more than that and they are essentially getting you to foot the bill for the advertisement.

Although, I agree with Deneidez, there are enough people who would probably be willing to buy this crap. Just look at the playstation blog suggestion area where every single suggestion has "i'd be willing to pay, just implement it." Not only that, but people buy/preorder games to get into beta's or play demos. The videogame industry seems to be filled with tons of raging gamers who love to waste their money and have their hands on things NOW.