The steel is different but I think it's also something to do with Central Wheel's threads and nipples too. Generally the rear uses 8 gauge and front uses 9, it is possible to get 8s in the front too but not many folks bother.
Sid's work is good. I'm not sure but I'd expect uses Central Wheel spokes (bought as blanks or maybe uncut wire).
Something to bear in mind is a complete wheel will be much cheaper than buying a hub, rim, spokes, nipples, bearings, seals and spacers.