I would like to say that sounds are not as they would be in real life. Some cars may be close, but there is a peculiar thing PD has done that I will get back to in a moment.
I found this by accident, as I was racing, that A LOT of the cars really do have proper sounds, but only in certain circumstances is there. I was using the Light Car Company Rocket, a very small and low (this is key) car, which is also fast. I had thrown a stage 3 turbo and a custom transmission on it, to keep up to those high powered cars in the A class 500PP races. When you are using more regular sized cars, you won't be able to replicate this as good.
Now, take to the track. In my race, I was at Mount Panorama, with everything between Elises, M3 GTRs, Jaguar XFR (I think), S4s etc. Many cars, both from previous titles and current. Now, as I was driving, with roof cam, I was riding the rear bumper of an NSX, when I heard the godly sound that is proper exhaust notes. I started to go past the field one by one, and get inches off the rear bumper of every car, and each one had the distinctive sound of that car. No vacuum cleaners. Each car was unique, and sounded like the real life counterparts in most of the instances.
This leads me to believe that PD did fix the sounds in one way, but there came another problem in the process. The sounds fade out much too quickly by the distance between the camera and the exhaust itself. Go try it, win the Rocket from the first tier of Goodwood, slap a bit of power and a tranny on it, and go hunt cars down. I tried it with an NSX afterwards, and it proved my initial thought. The nsx was to high (
), and rival cars was hard to make out.
The odd thing for me, is that chase cams is also affected heavily, so you won't get all that sound from your own car. If there was a patch that reduced exhaust sound dissapation, I do believe that much of the problem is solved!