Compare the range of products and pricing offered on Amazon (UK) for digital radio (searched for as DAB radio) to the equivalent search on Amazon (US), (searched for as HD radio), noting in particular that most of the items on the latter list are not digital broadcast radios. There are certain technologies that the US is just not very good at.
UPDATE: The selection does improve if one considers receivers for audio-video systems, such as this Onkyo model, but then the decision to get a digital receiver becomes tied to the decision about one's sound system -- and also it fixes the listening to one's home, defeating one big of advantage of radio.
FINAL UPDATE JUNE 2007: There's now a $60 DAB radio in the US. Hopefully a bigger market for receivers will promote a bigger set of DAB choices.