The reason there are no BMW M-Cars, or Porsches, Ferarris or Lambourghinis in the Gran Turismo Series is because they are licensed exclusively to the Need For Speed series.
GT4 will be released in North America. It was the GT3 Concepts that was a Japan only release.
I think the reason GT3 had a reduced variety of cars versus GT2 was not because automakers didn't want to pay to have their cars in the game, but because the game makers didn't have the time or money or desire to program in all the extra, basically useless (non-performance) cars that GT2 had. GT3 was released almost a year later than they wanted to release it, can you imagine how much longer it would have taken to release if they included Cavaliers, Sebrings, Taurus', etc. Sure they included alot of useless stuff like the Echo (or whatever it's called in Japan) and several other minicars, but that's because it's a Japanese game, so they're going to include more Japanese cars. And while I agree that this game is great advertising for the carmakers, they most certainly do not pay to have their cars included in the game. Sony (or whoever makes the game) has to pay a licensing fee to the carmakers to be able to use their car in the game. Think about it. Do you think Ford pays Hot Wheels for every Mustang dinky car Hot Wheels makes? If the carmakers were paying, then Porsche, BMW, Ferarri and Lambourghini would be in GT3, and not limited to NFS.
Bob
P.S. Don't forget about the 427 Cobra when talking about how many Fords are in the game.