There is some discussion of it over at the AVS forum.
Many users are pretty negative about USDTV because it is said to use bandwidth that is assigned to existing OTA digital channels, such that those channels may be unable to broadcast in full HD.
For example, I live in Albuquerque, one of the test cities. USDTV is working with the local UPN (or is it WB?) affiliate. As such, the local affiliate will not likely have enough bandwidth to broadcast any of their network content in HD (like Star Trek - Enterprise). Time will tell, I guess.
Those of us that are starved for as much HD as we can get are not really happy with the prospect, although it is completely within the law to allow a station to use its bandwidth for anything, so long as they are broadcasting digitally; no HD required, unfortunately.
Perhaps there are some actual user posts at AVS that can better address your specific inquiry.
Rachel, You are correct. I saw this receiver for that low price and then went back the next week and they have an LG receiver for $398. sitting side-by-side the USDigital. I know that there HAS to be a difference, but I don't know what it is.