Fuses in anything are mainly there to protect the wiring. Often times replacing wires that had the insulation melt or wires fry due to a short are much more difficult to replace than a simple safety device. Picture having to replace a set of wires from the dashboard of your car to say, your headlights. What is easier to replace, the wiring or the fuse? Add in the fire hazard of burning wire insulation and you'll get the idea.
Having no fuse in an AEG, as said above, really just eliminates one thing that can go wrong while you are using the gun. It doesn't protect anything inside the gun at all, just the wiring. I've gotten gearboxes that fragged themselves, gears chewed to hell, and the fuse never blew. The gun will work just fine without a fuse, and might actually see a slight rate of fire increase due to the fuse having a slight resistance compared to the wiring.