Why?
I can see in this case when size is an issue, but do you believe this as a general rule?
Isn't there low freq. material in 7 channel stereo and movie sound effects?
Bigger woofers could in some cases fill in the midbass couldn't they?
Not every one is a "set it to small and let the sub do the work" kind of person. If I had the room and plenty of amp power I would have low furiture and floorstanders all around set to large and 2-4 subs to boot!!!

If your going to make a theater make a theater! (I'm back from dreamland now)
not trying to start an arguement Sheep. Just curious.
SBF1