As has been said the premiums have been recorded in real life. As has also been said the game goes to great lenghts to reproduce sounds accurately, however here lies most of the problem.
In real life theres always random chaos thrown into the mix that influences how things end up sounding to you. The way your head, mouth, body, helmet etc vibrate will influence this, especially lound ones. Even your eardrums can be overwhelmed and distort erratically, no to mention the sound are interacting and bounding of millions of objects.
GT5 ignores this. What you have is clean undistorted sounds polished off by too much digital clean up and very basic reverb mechanics, whilst other game puposely introduce messy distorted sounds, and whilst beibg less accurate, end up sounding more raw.
I agree with OP, I would love to love the sounds, but I dont. They are pretty cold, lifeless, digitized, artficial etc. They and are missing substance or grittyness.
That said they are still great with the right setup, but not spectacular.