Most bookshelves and towers do not reproduce much frequency range below 30hz, I have yet to come across any good sounding towers handle bass down to teens, which is quite essential for HT nowaday. Couple years ago I had the Acoustic Research AR1 running off of the Odyssey Stratos for almost 2 years, the AR1 loaded with side firing 15" active subwoofers powered by built-in 500w Sunfire amps, back then I didn't feel the need for additional sub because they were being use 100% for music, and two 15" were plenty in my living room so I didn't feel the need for an additional sub.
Now with the M22ti, I don't think I can do without the Sub. In my room the M22ti alone can only go down to 50hz, anything below is mute so I'll be missing a whole chunk of stuff between 50 to 10hz, in my case...an additional sub make a complete system.
