I am sure that the reason for the larger outlet is for the people who install V8s in there trucks, that need more fuel flow.
I suspect they just figure people will use an adapter to fit whatever size one needs.
If they expected people to do that, at least they'd use pipe threads in the outlet instead of some weird threads that you have to hunt to find an adapter. With pipe threads, it would be a snap to adapt the original 1/8 NPT threaded outlet. You can find a bushing just about anywhere.