Correct me if im wrong, but Shermans were also prone to this happening weren't they?
I've read some accounts of Shermans have they turrets propelled right into the air when under fire from Tigers.
Generally when a tank was hit by an armour piercing shell, it would make a nice little hole, of the same size as the shell calibre. Sometimes the armour plate could fail catastrophically, but this was due to manufacturing defects in either the structure or due to the alloy being brittle.
If a turret was "ripped off" a tank, it was due to an internal explosion of the magazine and/or fuel. It wasn't due to the shell physically knocking it off.
The 88mm projectile used by German was (off the top of my head) about 20lbs and had a bursting charge of between 45g to 60g (depending on the exact type).
This shell isn't going to "rip" a turret of a tank.
The bursting charge was so small because it's purpose is to destroy the shell, not to directly destroy (the internals of) the tank by an explosive force.
The other reason to keep the bursting charge as small as possible is maintain the structual strength of the shell while penetrating the armour. The size and shape of the HE filler on early Russian 76mm shells was a contributing factor in the problem with the shells shattering.
Will post pretty pictures of tanks later.
EDIT:
These pictures are of shattered (brittle) armour on Pather tanks. The damaged areas are larger than the shells that produced them.
Pics originally posted by Wokelly
And a T-34 who's fuel tanks have exploded.
And T-34 after the magazine exploded.
And a KV-1 after the magazine exploded
And a KV-1 hit in the turret by an 88mm