I think all of the wheel modules I've seen online have had their main housing either welded together or machined from solid.
Our modules are bolted together using aircraft-grade 6-32 machine screws.
http://www.chiefdelphi.com/media/photos/32573
Don't get me wrong though, I'm a big fan of welding. It just seems to me that it would be easier to do service work on a given wheel module if it could be taken apart. Using screws to fasten the parts together does offer a serviceability advantage IMO.
I also believe that the weight of bolted housing is comparable to the weight of a welded housing - our modules weigh less than 4lbs each.
Still, the best wheel module is one that's so reliable it doesn't need to be serviced very often, or even at all!