But, many people around here have mentioned how when they run their m80's or m60's as large speakers with the sub off that the bass just seems quicker, tighter and more well defined. Many of those guys have Axiom subs. Granted, running no sub will not have as much low end extension as running a sub.
Most likely due to the fact the lower notes overshadow the higher frequencies, making it harder to hear the mid - upper bass range, especially if the room is sucking out some midbass etc. all the while emphasizing a lower range.
There are even some reviewers that always run their systems sub-less and mention the reason that they do this is for more musical well defined bass.
For the samre reason I noted above.