Over the next year or two, Comcast will finally catch up with all their competitors in that regard, and present cable networks (TNT, USA, CNN, ESPN, etc.) in digital, requiring a box on every analog television. In addition, just like all their competitors already do, they will likely encrypt most of their advanced services, to discourage theft of service.
What they won't do is encrypt basic cable, i.e., your local over-the-air broadcast channels (ABC, NBC, CBS, Fox, CW). Those channels will remain in-the-clear. In addition, until at least 2012, they'll be providing those local over-the-air broadcast channels both as digital and analog signals, so you'll even be able to tune in local over-the-air broadcast channels with older televisions, without a box.
At least. A lot of it will depend on just how much money they're allowed to make on the analog service. Currently, that level of service is strictly regulated. We pay $8.50 per month for it! I haven't read of anywhere where it costs more than $17 per month. It's basically a money-loser. If the FCC changes the rules, though, and allows MSOs to charge extra for analog service (while still providing the local OTA broadcast channels in digital, for that regulated monthly rate), that might prompt MSOs to keep analog service longer.
Thanks for the help. Comcast is giving my set top box for $9.99 a month with 2 months free but I'll get a bunch more channels. Going to start another thread with another question that kind of goes completely against what I posted here.