I did a cost analysis of Comcast a few years ago for a job...
The cost for basic cable vs the fee they charge if you dont have TV service is the same (I think NOT having TV is a buck more).
They do this not only as a money grab but it saves them $ because a tech doesn't have to come out to your house to put a filter on your line to block out the TV if you ONLY subscribe to internet service.
Its the same way with Phone Service. I have everything they offer and its cheaper for me to KEEP the phone then not to have it. (essentially the phone works out to be free..)