OK, so Dan Rather is leaving CBS, and word is he'll most likely be joining Mark Cuban's HDNet — a cable network available only to people with HDTVs. Rather told the Times' Jacques Steinberg over the weekend that he also had two offers from "major broadcast or cable networks." As there's no obvious reason he'd go to a network with no existing news division and distribution to only 3 million homes, we've got to assume it's just because Rather really, really wants to appear in high definition. But why?