In some cases and at some times in the past it was actually cheaper to get the internet service when bundled with Cable TV service. In effect, some are or were somewhat paid to get it.
The cable company pays a per-subscriber charge for come channels (most notably ESPN). For others (like HSN), the broadcaster pays the cable company. If they can get you to sign up for basic cable they're still making a bit of money, since all the ones they pay for are in higher tiers.
If you have internet through your cable provider they already have to make sure the signal gets to your house and you're already in the computer, so adding you as a TV subscriber costs them nothing at all.
I never watch broadcast TV, but when my internet connection goes down it's a handy troubleshooting tool - when I flip the TV on and see car commercials it means there's no cable break.
