You know, IRL drivers have to take damage seriously and moderate their driving accordingly. If you look at most races, especially the longer endurance races, the fastest laps are the qualifying laps because they have less traffic and they are only pushing hard for a couple laps. The cars would break if they pushed hard for the whole 12 or 24 hours, and as a result, in-race laps are run more carefully, getting the fastest possible time out of the car without pushing it to the breaking point. Lots of cars break without even taking crashing into account! The 12 hours of Sebring was a great example of this. The C6R was leading, and suffered a catastophic brake failure sometime after the 8th hour. The driver managed to slide the car sideways into the tires, and limped back to the pit in time to get it fixed and still finish 2nd. There are always wrecks, but the real problems are when something breaks on its own (tranny, brakes, engine). Especially the lemans races--collision damage is less than half the problem, and I don't think any of us want the PS3 picking at random who to curse with a blown engine or fried tranny. But that's what it would really take to make it real. And besides, what race car actually has metal body panels? They are all composites, and they bounce back or crack and break off and flap in the wind--they don't crumple or wrinkle.
Since this is, after all, a game, Do you really want to have to race a race agian because your car just up and broke? And what about class restrictions? There are 4 classes in lemans (I'm pretty sure, P1, P2, GTS1, and GTS2). Each class has horsepower and weight restrictions, and weight "rewards" (penalties for winning--arguably implemented to even the field) that are applied to each class and the winners of each race. P1 is usually dominated by the Audi R8, and GTS1 has been dominated for the last several years by the Corvette C5R (and now the new C6R. Which, by the way, I'm bugged didn't make it into GT4). Do you really want to have to race an Audi or Corvette to be competitive? I drive the vettes because I'm a vette guy, but I'd be pretty chapped to have to drive it to win if I didn't like them.
So, the question is, how real do you want things? I would really like better outlined classes, having to meet all the real-world restrictions. And I would even welcome BOTH types of damage--but as I've stated, it is always a gamble to drive slower, keeping your car in good shape, and hoping the people in front push too hard and break something or crash. That is a fine line, to intentionally NOT drive as fast as you can, saving gas, tires, and wear and tear on your tranny, engine, and brakes in a hope to be able to pick it up and close the gap if you find yourself behind still with 10 laps remaining. But that is WAY too real for most people. In fact, outside of the types of racing I like (lemans, trans am, and some touring car), it is too real for me! I have no interest in having to understand that for race series I'm not in to. And in my opinion, its all part of the same issue. There simply isn't enough benefit for the one without the other, and there's not enugh benefit for them both together for it to really be marketable.