I saw the same commercials. They are dated, though (but might have been produced recently). DTV stations have been multicasting for years now. I like the service, but I don't like the term because of its very different meaning in other technical arenas.
It's just referring to digital OTA subchannels you probably already get. Usually it's just an HD and an SD version of the same analog broadcast. For example, if you have channel 7 in your area, the digital broadcast might contain 7-1 and 7-2 (or 7.1, 7.2, depending on your receiver or TV). As the website and the commercial mention, though, in some cases you'll have others showing 24-hour weather radar or something (BFG's area shows The Tube on a subchannel!
). PBS stations tend to do much "multicasting".
Like I said, I like it, but only when used "responsibly" by the station. Each subchannel needs a certain amount of bandwidth, and that bandwidth comes from that which could be needed by the HD channel to maintain good picture quality.