The low poly models are very noticeable in replays and ingame when you are close to other cars in cokpit/bumper view: blacked interiors, simplified modeling, less details, half resolution liveries, etc..
I'm gonna have to be honest with you Zer0. I don't question your findings at all. Seems like you have extensively researched the shortcomings in this department. And I hope it's something that can be addressed. However, and this is truly just my opinion and my experience with the game, all of this really doesn't come into effect when you're in the heat of the race. I honestly don't notice any of this when I'm racing.
These are the things I noticed while driving each of these games for first time and a while.
Forza 3: The jaggies stood out to me. I knew they would and I wasn't surprised by it. Everything else I never noticed. The liveries looked spot on while I'm in-race as they do when I'm doing a photo. Whatever Turn10 did they did right because , I really feel that unless you're looking for something like that you're not going to notice it.
Race Pro: I immediately notice the graphically hit. Kinda hard not too but hey they never professed it to be the best graphical game to hit the market. The other thing I noticed right off the back is the game has trouble making the color "white" on the sides of vehicles. It's weird but the colors go metallic to flat to ... I don't know. Is it a big deal? Not really. I wasn't going into this game to be wow'ed by graphics. I was told it was all about the physics and the racing and they were right.
GT5: Everything was fine right up until I saw my first shadow. Now I was expecting to go outside get in my car ,drive around, come back upstairs get on the PS3 ,drive around, and not be able to tell the difference. Well that got crushed right away. The visuals were great but the shadow totally took me out of the immersion. Then you had the track lines , in-game mind you, that are sometimes not smooth as if the guy who paint the white lines was playing connect the dots. THEN the standards came into play and I didn't know what I was looking at. Look at one section of the screen and it looks great, move your eyes over here and it looks like 8-bit shadows , move your eye over here and you're pressing eject on your PS3 to make sure you don't have GT3 in there.
In otherwords the consistency and fidelity of the graphics is what makes the game. What's the use of having a car that looks like it came out of a photo running next to a car that looks like it came outta Sega Outrun only to run on a track that sometimes goes from GT5 to Pole Position.
Even with Race Pro graphics I was fine except for the "white" metallic issue really threw me for a loop and took me out immersion when I concentrated on it. But other than that the consistency was there.
This reminds me of NHL 2K5. Graphics were all over the place. The ice was beautiful. I mean it looked like an actual photo of an ice rink. But the players were all jagged to death and the color palette must have been about 256 colors next to the millions in the ice. It really stood out and just killed some of the enjoyment.