Yep, this is the case here as well. Paying Comcast for TV + internet because it's $15/month cheaper than internet alone. The cable box they sent me is sitting unpacked in the closet.
Fuckers.
Interesting, do you have another provider in the area?
I think a lot of the negotiating power comes from the ability to threaten to switch to <competitor>. If they know there is nobody else (and in many places in US there isn't), they can often say "yeah sorry to see you leave", knowing that you can't really go anywhere.
I have for example been oscillating between two local providers. Both have equipment on "premises" installed and just have to switch it on and off. So as soon as one ends promotions, I switch to another and do so on. Sometimes they give me the promotion rates back without having to go the full switch around the circle.
Promotions usually run 6 month to a year.