TB, Bubi, no matter the 30 was a hard hitting cannon, prolly the best A2A used in WWII (IIRC Tony Williams said so in one of the articles on his website), but, on the other hand, no matter the B-17/B-24 were hard to shoot down. Take a look at the page from where I took the second picture:
http://www.daveswarbirds.com/b-17/I'm not saying that hit shouldn't have left damage, I'm just convinced that damage was correctly recorded by game but it wasn't enough for the game to display it graphically. It's a matter of graphical detail, not damage recording.
And, yes, I'd like to have a better damage displaying system in the game, something like the IL2 system (talking about graphics only!); and I'm confident we'll get hit, in the end, HTC already begun updating it with the redone planes. Last week I was flying an IL2 chasing tanks, I was (pleasantly) surprised when I took a hit on my aileron, turned the head to see it and, instead of the usual square gap, I saw twisted metal ribs coming out of the spot where the aileron should have been. Give them time, I'm sure they're working on this issue, too.

(Can you confirm that it's just a graphical issue, HTC? And, about the bill for my performance as your lawyer, I'll just accept a lifetime long free subscription, thanks.

)