I don't understand why you'd want a weldless setup with washers/orings to leak or melt instead of a welded setup, where you don't rely on orings to keep your pot from leaking.
Not going to start a flame war, but I hate seeing this type of miss information out here. If you are melting o-rings you are either firing your kettle without water or wort in it, our you have your flame way too high. I would be far more concerned with melting the deals in a ball valve at this point.
As far as leaking, I have been brewing with weldless fittings for 10+ years with no issues of leaking. The only thing is to have a properly designed weldless fitting.
If you want to get into exposing negatives, a problem with welded fittings is if you get galling, then your fitting is toast, or what if you strip or cross thread it? Most people also fail to mention that most homebrew npt fittings are sealed by Teflon tape.
IMHO the only true foolproof fittings would be welded tri-clovers like the pros use, but those cost $$
Again, welded or weldless, your choice, they are both suitable and reliable methods for putting fittings on kettles.
For the record I use weldless, mainly due to market availability of welded fittings just now hitting their stride. I also think spikes new kettles look great, and if I had to do it again, his new kettles would be on the top of my list. I brew with blichmann kettles as I got great deals on them, and they have a great false bottom only equaled by spike.