Geez, Ken. You know I'm just a humble beer geek trying to navigate the treacherous waters of the home theatre ocean.
Sonically, I'm sure you're right. I was trying (feebly) to differentiate based on market placement. The M40 and M50 are not the "ultimate" Axiom towers and the M2 and M3 are not their "ultimate" bookshelves. Anybody who, for whatever reason, is predisposed to tower speakers, has a budget and discovers Axiom is likely to look first at the M40/M50 models.
Obviously, I'm committing conjecture among scientists. I'll be burned at the stake eventually.