The only advantage I can see to bent handles is that they will always fit the same way in the hand; straight ones would be rotatable. Given high-density foam on the handles, they will likely develop a bit of memory, so that they will be held exactly the same each time you fly. Or am I spouting utter crap?
It's a good question, the Airbow has symetrical handles but I have seen quite a few people flying it with the more traditional Rev style handle.
I have tried various handles some that are straight and some that are bent very near the top. None of them felt right to me but that may be because I have spent 10 years using the other type and 10 minutes using the straight handles.
However, I believe the bent handles makes the neutral holding position more comfortable than straight handles.
Mind you, has anyone tried a kite surf bar yet?