Not that Hulk using the car bothers me at all, and I don't know if anyone has already suggested this but...
The clip suggests that Hulk has already been slugged one by Abomination (it looks like he is just getting up as Abom steps over the bus), now considering he might just have taken a very good punch (good enough to send him flying and put him down momentarily) and seeing Abom is bigger than him and likely has a considerable reach advantage, one that Hulk can see he has trouble getting past, maybe he uses the cars simply to boost his own reach? He does use them to both block and punch in that sequence.
Just a thought, and like I said, I really aint bothered bothered by it: Whatever the rationale behind it (or lack of, as the case may be) it makes for some great superhero slugfest eye candy.