bombs actually do have blast effect on a tanks..
Though, effect is usually wrong.
With bombs, it seems more like tank either blows up or doesnt, not many times it just gets damaged.
I believe that if 1000lb class bomb hit somewhere nearby, tank might not have blown up, but had severe damages.
I've seen many times when 1000lb miss makes bomb blow up..
Once there was players tank stuck near to airfield, weren't shooting back and I dropped bombs on him in all the joy of it.. as I got second kill of him, I began wondering whats up with this osty, asked the guy is he there - he was 10 miles away really, not there where I were bombing him all time.
I did drop twice one 500kg bomb (1100lb..) past the tank and it blew up. (hit was far off)
I've also drop 4000lb bomb like 50 yards off a tank (i bet it was more) and it blew up nicely.
So much for no blast effect on tanks

I did once disable tracks of M3 halftrack with panzers 75mm HE round which was close hit on the ground