Here's my view on this. I think that all of the damage is still there. I just think that since cars are a much less dispensable than in IV that they allocated more damage to be done before the visual damage its. Remember you have to pay for a mechanic to repair your cars. There is obviously damage in the game, and we've seen cars that look bent and everything, but there is the fact that Franklin was driving the car. There could be less damage taken to the car with him in it, as well as the possibilities of this car being a bit reinforced.
They also probably tried to make the damage a bit more conservative because often in GTA IV you hit something and you get a completely inaccurate depiction of damage on your car. I don't think it's gone, but it's obvious it isn't the same a IV. I do know that we don't have enough evidence either way to make a logical determination on the stance at this point. We have two isolated cases and don't know more than 3 seconds worth of damage to cars.