It's been discussed in these forums in various respects quite extensively, but no one generally owns any equipment to produce remote productions. The networks rent mobile production facilities from a variety of vendors (for several reasons). Secondly there are only about 52 HD trucks on the road right now, and most of those are snatched up by long term agreements with the big networks for sports. Thirdly it can be quite a bit more expensive to produce a show in HD over SD not just from the added cost of renting a more expensive remote outfit, but post-production costs, HD animation packages, uplink trucks that can send out HD, tape stock, often recabling of stadiums (especially college), HD friendly makeup and on and on. And on top of that the network may not have the integration facilities to even send out an HD feed. All these challenges represent major capital investments, many of which are in the process of happening as we speak, but many are also dictated by the market and whether it is truly profitable to produce an HD show that is going to have a tiny audience.
