said by wanabdigi 
:I have had Comcast basic for years. I just baught a Sony Wega HDTV ready TV and for some odd reason, I can get HDTV channels. When I look on Comcast's web site, it appears that you have to have digital cable ro recieve HDTV so why am I getting them?
I get CBS and PBS in 1080i(16:9) and all of the rest of the local channels in 480i(4:3). One other weird thing is there are other digital channels and one of them recieves what appears to be on-demand becuase I can see soemone fast forwarding and reversing it. Believe me I know it is on-demand becuase it is not suitable for children.
I hope someone can explain why this might be happening?
I don't know about the OnDemand part, but you probably have a DIgital Cable Ready TV (ie a Cable Card TV). The channels you are seeing are the unencrypted Local HD stations. Typically you only need the Cable Card itself when you subscribe to a digital package because digital packages include encrypted channels and the digital box that is built into your box decryption codes for the channels you subscribe to.
The On-Demand data stream is carried on a node's randomly generated sub-channel by the time it reaches your DCT. A digital TV has a built-in QUAM demodulator that can lock onto the signal, which Comcast hasn't bothered to encrypt just yet. As digital TVs see more market penetration, the cable cos. will catch on & take steps to encrypt the signal so that only the person who ordered the On-Demand movie gets to see it. In the mean time, if you happen to have a Digital QUAM 256 decoding TV & you're on the same node as a person watching On-Demand, sit back & enjoy the ride! You can't control it, you can only watch, so enjoy it while it lasts. 