Why aren't you a fan of subs?
Full range speakers reproduce sound from 20 hz to 20,000hz without more than 3db deviation. M80s can't do this. In fact, there are very few speakers that can. Much more power is required to produce low frequencies than high, so a passive speaker (non amplified) capable of full range sound production would require some great honking amplifier.
It makes a lot of sense to relieve your speaker (and amp) of the stressful task of producing sub 50hz output.
Also, just because a speaker puts out low frequency energy that shakes the house doesn't mean it is producing music. I have heard some speakers which flatulate loud enough to shake the house, but which sound more like the mens room at the sumo dojo after baked beans dinner than music.
