True.
I cannot believe I just now understand that concept!

I need to think bigger.
This is why I stick around here; I learn something new every day
I've been using them without a sub for a while.
If they extend flat down to around 50hz, that means i'm missing roughly an octave of bass frequencies until a subwoofer is made. However what bass is there is like 95% of the bass we hear in music. I wouldn't even contemplate making a sub if i were just trying to get down to all audible frequencies - for 800 dollars this things put out excellent, loud bass from 50-200hz.
But i at least have a place to put them. On the floor. Where they stand. As floorstanders.
Also, could ya name a 800 dollar bookshelf with 88+db sensitivity which extends down to 70hz with ~200 watts of power handling? Also, there's the fact that towers shouldn't be called upon to do deep bass anyways - in that the best placement for imaging ain't the same as the best placement for bass in most rooms.
Besides, you could probably take some monster tower speakers like the revel ultima 2s with F3 at 23hz and still probably want to pair with a sub placed somewhere else crossed around 60hz or 80hz for the best sound in room.
In fact even a low crossover frequency in a passive 3 way design is undesirable in the first place for complications that introduces. Why even buy speakers with passive crossover period? We should all be buying fully active speakers and 3 amps to pair them with!