Hey brian,
I understand your opinion and I agree that there are a lot of "details" about this game, which are wrong. It is not an accurate simulation of every track and every car, and in stock form a lot of these cars are wrong (same was true with Shift 1 - it had a decent engine, but wrong data). Same goes for track width and all the rest.
I think most people playing this game have not actually driven a gt1 or a gt3 car, so people would not know a difference between how a Sumo Power Nissan handles vs. a Corvette. They might have a general idea, but very few people have driven them personally. So, what I'm saying is this, this game CAN be made A LOT more real if the proper data is used, which was shown by the Overhaul mod for Shift 1, which corrected A TON of bugs and inaccuracies with the vehicle data in that game, plus other various bugs. Whether it will be or not is yet to be seen. However, most people play games for fun. We are not all Tommy Milners or Mario Andrettis, who would use a game as a simulator to train for their races.
I completely agree with you that many cars may not handle like the real thing, however this does not mean that the game is not fun, nor does this mean that the game cannot be made more authentic by going through the data and fixing it or tuning cars. Look at GT5: many things are more "authentic" and even you rate it at "3" vs. a "2" simulation wise, however it's boring as hell