Dean,My guess is that you don't "need" a subwoofer.
That said, I've learned that a good subwoofer can be an awful lot of fun, particularly with movies. I'd never heard (much less owned) a subwoofer and recently built a Tempest. It's really a hoot when movie LFEs kick in, causing the whole house to shake! For less than a $500 investment (including driver, plate amp, MDF, veneer, etc.), it's giving me a lot of pleasure.
(BTW, I don't mean to imply that the Tempest is just a rumbler. It sounds great w/ music as well, subtlely filling in the bottom octave.)