Ferrari's own (horribly arcade-y, I must add) game basically says it all:
They don't want damage.
They don't want police.
They don't want the wrong potential customers getting a bad impression (ie: their extremely arcade-oriented game had so many assists you could almost drive around the track without steering; literally.)
That's "Ferrari Virtual Race," by the way. I'm guessing Ferrari one of the main reasons GT5 will have damage on some, but not all, cars. It's a bad plan, really, for Ferrari.
More and more games are getting damage, and Ferrari really should realize that some of the gaming generation will end up being potential customers (though, admittedly, not many), and if they continue to shy away from games where there is damage, those potential customers will go to Lamborghini, Porsche, and now Nissan (the GT-R), ignoring Ferrari's treasured heritage in favor of dream cars they are more familiar with.
-Leadfoot