This from 2008 A Banner Year in Sports?… (http://www.nielsen.com/solutions/YearInSports_2008_MF_rev.pdf) (.pdf file from Nielsen)

High Definition became essential for sports viewing in 2008, providing a crystal clear digital picture that puts fans in the middle of the action.

By October 2008, HD televisions were in 22% of U.S. households:

Sports programming is more popular with HD viewers than any other genre according to an index of Nielsen’s National People Meter