Quote:
Originally Posted by Raptor1
Indeed. 
Oh, do note that some Assault Guns, such as the KV-2 and the Churchill AVRE, did have turrets. Though they still don't really count as tanks because of their low velocity guns and specialized design. |
That has a lot to do with the designation - a low-velocity primary armament almost immediately defines the vehicle's role as indirect-fire capable infantry support. AT Guns, TDs, and tanks are direct-fire weapons (not saying they can't be used for indirect fire, but that's not their designed intent.)
Assault guns (esp. the short-barrel 75s) can fire both direct and indirect missions using the same primary weapon with little to no change in operation.