There is a lively thread at Hear 2.0 about HD Radio.
Stephen Hill has a characteristically long comment, highlighted on his blog.
The most interesting anaolgy I thought was that of HD Radio multicasting and UHF / VHF television. Buyers at one point had to make a decision to buy a TV set that could either get UHF or not. Then it became standard, and now the kids would not know what we are talking about, having grown up in households without two channel knobs on the set.
HD Radio could follow the same path. HDTV has done some of that already. First the TVs were HD compatible, labeled “HD-Ready.” [Much like cable-ready, from so many years ago.] Then they had tuners built in, and soon, there will be no distinction.