...and it never happened at all.
How do you know it never happened? You mean you have never found any documentation or recorded instances that it happened, but the possibility is there reguardless of if you think it did not happen.
Yes, I agree the odds of it actually happening in real life are slim, but being the possibility is there, it could have happened. I have killed many B25s and IL2 coming at my tank, head on at less than 25% off the horizon flying perfectly straight and level... 600 Bingo! your dead. Probably never happened in real life because in real life the pilots were smart enough not to fly that way at a tank. Wouldn't expect a plane to be taken down by riflemen ground fire, but it happens, ask the Red Baron.
I think the reason it occurs so much in the game is simply due to the fact that more pilots fly low and slow straight at tanks to try to turrent or destroy them, therefore the occurance increases. Whether it is a .303 or an 8 inch, if the path of the projectile meets intersects the path of an aircraft, the damage will occur.
My $0.02 worth.