The Milspec tube is supposedly machined from a forging -
The commerical tube, at least in the past, for some companies, are extrusion tubes wielded shut at the end
I here this a lot and I don't believe it to be true (not offense GT

)
A) extruding is a form of forging, it's just like the 'play-doh fun factory' instead of hammering it between two dies.
B) I have never seen, nor has anyone been able to show me, an example/picture of a tube that has a endplate welded on
C) You would be able to visually see that something had been welded on. Anodizing hides nothing, whether it's clear, colour, hard, or black-hard, you will be able to see the weld like a sore thumb
Maybe a mil-spec tube is stronger,.but unless you're using your rifle as a pry bar or a baseball bat, you're never going to have an issue. That being said, Mil-spec is definitely cooler
ADDED
the threads ARE full diameter on a mil-spec tube as opposed to 'topped' on a commercial - this is the source of the 'weakness' of a commercial tube as opposed to a mil-spec