Many cable co. are now sending out their HD local channels (as well as SD digital subchannels & other digital channels that are part of broadcast basic cable) unscrambled, which means that all you need is a digital cable-ready TV &/or box. A cable-card TV is considered digital cable ready, but because the signals are not scrambled, you don't need the cable card to view.
Matter of fact, with some of these same co., if you have cable modem service, you could actually downgrade to NO TV service at all, but you still would get these unscrambed digital channels, since they are carried in the same part of their bandwidth as the cable modem service, which their cable modem-only traps do NOT trap out. (but there are some co. that DO trap out their digital TV services with these same traps - depends on your system)
On Insight here, we get all local HD channels, as well as 2 digital subchannels (PBS Create & local weather radar) & even all Music Choice channels, w/out needing a cable card, nor do you even need basic cable service if you have cable modem service.