Local radio and tv on my computer?

This morning I started wondering why off-the-shelf computers (Mac or Windows) don't include the hardware and software necessary to receive local AM and FM radio, as well as local television signals? I don't know the technicals hurdles behind this -- and that might be the problem -- but it seems like in our media-saturated age these would be standard computer features. (Hmm, after a little research it looks like this can be done, it just isn't.)