You do realise though if you took a film set in any big city (especially big American cities) and tried to list every single car possible you'd have hundreds of entries. I agree with antp in that having too many background vehicles overshadows the cars that actually used in the film.

One way I see this site is that it's like IMDB, but with cars instead of actors. The three and four stars cars are the main cast members, the two star cars and some background cars are bit players, backgrounds that gets into pile-ups are stunt players and most of the background cars are extras. Film don't list ALL the names of the extras in their credits for obvious reasons (we'll ignore all the real factors as to why some extras don't get listed because they aren't in industry unions etc. etc.)