It appears that is the key. From the article drummerguy posted:
The CEA is saying:
So it seems to me that both might be accurate. There might actually be that many millions of HDTV sets NOT connected to HD programming.
Heck, my own mother-in-law has a gorgeous 60 inch HDTV connected to an SD DirecTV receiver.

I've told her many times to upgrade to an HD receiver and she says "oh, I don't really care it looks fine to me". It makes me want to puke when I am over there and they are TNT "strech-o-visioning" everything. I changed the aspect to 4:3 and everyone was like "hey, I don't like those black bars on the sides, put it back".
Sigh.