Barrel extensions are the same. Bolts are nearly identical, enough so you can use a dpms bcg in an armalite, it's just advised to use the whole thing, and not mix and match parts due to tolerance stacking.
Old dpms and Armalite uppers are the same rail height, different thread pitch. Many companies made forearms, and only difference being the barrel nut. PRI, SWS, SLR, Badger back in the day, to name a few.
Gas tubes, Armalite made a longer one, which all 308 ARs can benefit from. It provides a better engagement of the gas key.
But your point on the designations is very valid, i personally think it would be less confusing if the "AR10" designation was used more widely, and the focus on differences be stated by manufacturer.
For handguard for instance, if they make the rail specs to the SR25, the rail portion will line up with Armalite, Old Dpms, and everyone that goes according to those specs. Which is Aero, BRO, Rainier, Mega, etc etc. In that instance, armalite is the odd ball with their different barrel nut threads.
So, theoretically, an SWS rail can be made one way, and have different barrel nuts for the different threads, which they do.
Having the numerous nomenclaturers furthers the confusion. Aero calls their's the M5, now people aren't sure if parts for an LR308 or AR10 will fit. Or the PSA PA10. Then you have the M&P10, with more proprietary parts. The mfgs seem to be purposefully complicating the 308 market. As well as small timers peddling out of spec parts, or just not holding good tolerances. Which is where you get uppers and handguard that don't line up perfectly. Or very badly.
This is why there will never be a standard, atleast not for awhile. Too many companies trying to capitalize on the market by putting out stuff that's proprietary. Leaving them the sole source for parts. Which really sucks.
The recipe for a good standard is already out there. But the mfgs week not agree on anything because no one wants to share their pie.