Much easier to aim your attacks. With a rear hinged, unless you're driving forwards, the robot could go more or less anywhere. With a front hinged you can deliberately send a robot somewhere, i.e., the pit, oota, etc.

It might not be so spectacular but I have always thought they're more controlled and strategic than rears. Think of Firestorm's success, and Envy's success! And Mute's general coolness. Andx2 the smooth self-righting. :P

If you design it well getting other robots to sit high enough on the arm for them to topple shouldn't be much of a problem.

Edit: and if nothing else, you'll be praised (at least in my book) for doing something a little different with a pneumatic system.