For some reason they record the engine sounds with the car not actually moving, they just rev the engine in neutral. Seems like a bit of a stupid way to go about things, but my point is it's likely (I haven't heard a Tamora since the guy in town got rid of his, which was ages ago) that if you compared the sounds of the game and the real car, as long as the car's not moving, they'd be quite similar. I guess. I think it's probably to save money and time, if you consider how many cars there are in the game and how many miles they'd have to do to get the sounds recorded, and I'd imagine getting the recordings of a Sauber C9 or whatever else at full pelt is quite hard due to road and wind noise, etc.
I had the same thing at this year's Festival of Speed; the Lancia Stratos and 205 T16 didn't sound all that similar to the cars in GT4, where they sounded, well, they sounded like they weren't really going anywhere. Because they weren't when they were recorded. Still, when they put the Tesla Roadster in GT5 at least the sound won't be too hard to recreate!