I'd say there's a lot to point to the Subaru scene being run on the engine, (if not necessarily in real-time on one PS3,) due mostly to the way textures are mapped and filtered onto the car, as well as the animation of the front wheels turning; although I suppose the latter could be lifted.
It doesn't look to me as though the two NASCAR racers actually touch, or maybe that ought to be "should have touched" - but it is close, and the #24 kinda pauses as the #14 comes through, but it had just fully re-mounted the banking by that point after getting a bit airborne on the right-rear, too.
I personally think the Citroën scene was an AI test (notice how everyone ends up on the grass!) and they (the devs / publicity team etc.) thought it looked pretty cool and whacked it into the vid. Disabling collision detection to test the AI is probably sensible in some situations, and the Citroën clearly "clips" through the 'Vette.