Jason; not sure you can really say that PU is the standard fabric in the US. PVC and Hypalon boats still outnumber PU boats by a longshot.
As far as tube makers, possibly you're right, as Wing is the only tube manufacturer I am aware of in the US (commercially, at least; I'd guess there are guys that do one-off jobs in hypalon around somewhere.) You apparently know of one other manufacturer. I don't. Still a sample of 2 is pretty small to make that kind of a generalization regarding a worldwide market.
I don't think there's anything inherently wrong with welding; I'd hazard a guess that most mass produced PVC boats are welded (at least the tubes are.) The big advantage to welding is that it can be automated - machines are probably faster and don't get paid as much as a skilled tube manufacturing tech gluing up hypalon, which helps bring production costs down. The tubes they end up with seem to last as long as hand-glued tubes, so I would have to say they'd be adequate, especially for recreational use.
The only real question mark I had was longevity, and that is proving itself as time goes by. PU seems to last as well as hypalon, as far as I can tell.
Bottom line: I wouldn't shy away from a PU tubed boat simply because of the fabric or manufacturing method.