Actually, the frames are usually welded and the skins are pop riveted, I believe. Even on that thread you posted (that rig was a work of art, btw), the rivets are mostly just for skinning, correct? I don't think any one here doubts rivets use for skinning.
Just from my observation on my bus, I have too many loose, wallowed out, rivets to rivet anything that will be hidden. Maybe I'm just arrogant and put too much faith in my welding. I am pretty damn good at it, though