If you discount salesmanship in the specmanship (a pretty generous stipulation) I'd offer the possibility that spectral balance is the most likely reason for the difference. You mention fooling with the sub level - the "impression" of adequate bass is enhanced by a boost in the area of 70Hz. Lower response around this freq will give the sense of lack of bass impact.I wonder what it would seem like if you eq'd them flat?
Hey, what do I know? I'm more of an amateur than you are!