It is late, I am tired, but let me chime in a little...
Some recent (last year or so) movie soundtracks have encoding for below 20Hz.
It doesn't matter if you have three 6.5" woofers in each speaker, they still aren't as efficient at the LFE as a 12" or large subwoofer.
Yes, you *can* set your front speakers to some crossover below 80Hz and get a nice lower frequency effect for movies. Heck, a lot of music lovers don't use a sub and still "feel" things like bass drums and such just fine... Those are generally in the 30-40Hz range for most music. (FYI that I have my fronts set to go down to 40Hz and the subs still start kicking in around 80Hz. That is with two 12" subs in 4cuft boxes each, shhhhhh... Don't tell anyone that my fronts are set at 40Hz.) I love how it makes things sound in the room.
I know of nobody with a home theater that doesn't have a sub, and there is very sound reasoning for it. It seems illogical to set your tower speakers to "small" and crossover to "80Hz" as usually recommended even with tower speakers, but it usually does sound better offloading the massive air pushing to a larger woofer than you are going to find in most tower speakers and those subs have their own power to make it happen.
