Hmm, it would seem that the bombers would have had the same amount of time for a shot as the 262 or 163 pilot would have. Actually, considering the .50 cal ballistics vs the cannons I think the bomber gunner may have had a longer shooting window.
Granted, the bomber was larger and less manueverable, so may have been an easier target to hit. But then again, the bomber gunner had a more stable platform to shoot from.
The closure speeds are really up to the fighter pilot, as is the approach angle. A faster approach gives less time to hit or be hit. A bad approach angle and speed would seem to be the fault of the fighter pilot, not the game...
MtnMan