^dangit, the forums broke earlier or I would have posted that.
The R2 slot isn't as wierd as it looks. Think of it like this: ALL of an R2 unit's internals (except what's in the legs) are attached to the head. When the head's in its normal position, the grippers/terminal probes/etc line up with little doors in the body, which are simply spring-loaded. There's a lock at the bottom of the torso internals that can be disengaged to slide the entire module out for maintenance/etc. The Naboo use the 'mech in that mode for the actual interface, probably because it allows more thorough systems integration.
This also explains a lot about R3/4/5/seven/ate/nine units, because popping the entire head+guts out to swap them allows the torso to be re-used as we see with those models.
