My local Comcast has effectively limited over-the-wire availability to the ultra-basic channel line-up. I can't even get the HD network channels without an external tuner that has an authorized CableCard.
So theoretically, these TVs should be able to tune in just about anything. But your provider has very likely seen to it that they don't. I really hate the cable company...."Hey, why use the tuner in your new $6500 TV when you can use our Motorola POS-HD??"