I read an article a couple months ago that said something like only 19% (not positive about that number) have HD service. I had HD TVs for a couple years before I switched. Don't remember why I bought them.
I wouldn't be surprised if this were true. Between 70-80% of American households now have at least one HDTV. That means that ~50-60% of HDTV's are being fed either an analog signal or SD signal. The service providers need to do a better job of selling HD service. The TV manufacturers have done the job of selling the physical product.
'just plug that cable line into the back of the HDTV and it will turn your signal into HD..... magically.'