To clarify, your initial statement said "a locked center diff" would be a valid form of AWD, which is what i was contesting.
All the differentials mentioned in your link allow for variable power distribution to each axle. Thats the whole purpose of a center differential.
Of course, not all AWD are created equal. Some apply equal torque to all wheels (i.e. open), some prefer a single axle (e.g. limited slip), some aren't controlled by the wheels but by the ESC (e.g. electronically actuated clutch packs). I suppose in electric cars where each axle is driven independently they dont even need a center differential (but I have no knowledge there).
But its an interesting link nonetheless - it was certainly educational - so thanks!
I do agree, however, that a full-time 4WD (which have a central diff, unlike part-time 4WD which generally do not) are effectively indistinguishable from an AWD with a simple open center diff. Of course, those are the least effective types of AWD - but the 4WD at least has the ability to lock that diff and likely has a multi-speed transfer case :)
