Despite HDTVs now being in more than half (56%) of the homes in the US, the overwhelming majority of TV viewing is still in standard definition. Nielsen reports that on a total day basis, only 13% of cable viewing and 19% of broadcast viewing is in "true HD" which requires an HD television and HD tuner that are tuned to an HD channel.
The reasons vary. Some home have HDTVs but haven't ordered HD service from their providers or are not set up to receive over the air signals in HD. Nielsen notes that since most home have more than one TV and not all of them are HD, that even in homes with HDTVs, about 1/3rd of the viewing still happens on televisions that aren't HD. Even on HDTVs that are "true HD" capable, about 20% of the viewing still winds up in standard definition.
According to Nielsen young adults age 18-34 are more prone to seek out HD content:
“True” HD Viewing on Cable Networks
(Percentage of Total Viewing in HD)
|HHs||Age 2-11||Age 18-34||Age 35-64|