Two reasons for towers. Some of us enjoy the pure/direct mode in our receivers and letting the towers deal with music down to their limits. We can still switch back to other modes that use the sub when watching videos. Second reason is efficiency and volume. Towers are still loafing when bookshelves are starting to struggle.
BTW, It looks like 3 of the 4 links are dead.
Family Rm: Samsung 52" LCD, Onkyo TX-NR809, Emotiva XPA2 & XPA-3 amps, PS3, Oppo BDP-93, FIOS HD DVR, Salk Song Tower-RT, Song Ctr-RT, Song Surrounds, SVS PB12-Plus/2, Velo SMS-1, NeoTV 550, Roku 3, Harmony-1
Bedroom: Hitachi 42" LCD, FIOS HDTV, Onkyo TX-NR906, LG BD370, NeoTV550, 3x Sierra-1 NrT (LCR), Boston VRX srds, Hsu ULS-15, SMS-1, Harmony-1
Home Office: Onkyo TX-SR707, 2x EMP E41-B, Emotiva Ultra 12 sub, and a small media server