I would have to check but from what I understand the cable companies are REQUIRED to offer the Over the Air stations (Or at one time they were) "In the clear".. now that was before Digital OTA,, with Digital OTA I see a number of "Tier Two" (That is #-2 or #-3) channels that DO NOT appear on the cable list.
IN fact I have my DVR's set to do mixed recording at the moment. Sometimes picking a show off Cable, sometimes off OTA. But I think they are, or at least WERE required to carry local boradcast in the clear..
OF course the Cable/Sat companies are trying to eliminate OTA broadcast, I do not think it will happen, but .. Well,,, It might happen.