the 17lbs lost the ability to look around with the great GV update in 2011. Before that, you could look around inside the tanks when being in their main gunner position. This was taken away, so that no interior has to be created with new tanks. The 17lbs is modeled like a tank turret as well (that's why you have a gunsight there), so losing the ability to look around was a (very unfortunate) side effect.