I also watch C-SPAN. That's funded by cable providers and available only to their subscribers
So I have cable with a QAM tuner TV. The guy at Circuit City said I could get digital cable without having to rent a box from the cable company with it. Turns out, the only digital channels I get are the ones that come in over the air. Is/was this supposed to change on Feb 17?
Nope. This switch over was for over-the-air only, and remains so even with this new legislation. Your first mistake was listening to the guy at Circuit City. There's a really good chance that most cable companies will never send anything over in Clear QAM other than your over-the-air stations. Everything else will most likely remain encrypted, and only received with a cable box or cablecard compatible set top box or TV.
I've heard (but not sure about) there is a 5 year moratorium on cable companies turning off their analog (cable-ready) signals. Who knows what will happen after that point.