Downloadable content is nothing new, Microsoft have been doing it for years with XBOX Live, which was the first console to actually get consoles online properly. Sony tried it with the PS2 and failed, monumentally. I don't mind paying for extra content that has been released after a game, especially if it's one I enjoy, but charging extra money for something that could be packaged with it is taking the piss a bit.
It'll be OK of Sony package the game with several hundred cars already (As with previous versions of GT). I'd hapily pay for a car "Package" containing cars I'd want. Packages such as "All Toyota cars" could be done. I wouldn't want to pay for an individual car, unless it was mere pence for one, which is unlikely.
Anyway, I shan't be getting a PS3 for a while. Certainly not until the prices come down a bit and there are more games available.