When I had a TiVo it didn't give just the channels I should be able to receive. It have channels another market over or two. I live west of Baltimore and reasonably even with a good antenna would get Baltimore, Washington and maybe some south central Pennsylvania. But that would be a very good antenna. My TiVo gave me as options Philadelphia stations. I don't think it is being smart about your market as much as they do a much wider area for any market.
TiVo used the Zap2it.com (Tribune) lineup for my zip code, and perhaps I should have clarified further...
Most every channel it offered me were channels I have received at one time or another. Only some of them were reliable enough to actually add to my guide though. If I had a 30 or 45 foot antenna, I might be able to receive most of them... heck, I might even be able to receive all of them... that is until the antenna gets struck by lightning.
The important thing is that it offers me guide data for ALL the channels that I can pick up reliably, and some that I can pick up sporadically... some REALLY sporadically. However, I'd much rather un-check channels with guide data from my channel list that I can't receive, than not have the guide data on a ton of channels channels that I can receive.
So... I'd love it if DirecTV went by that model... and if they couldn't via satellite, than maybe via broadband.