Leno's Ratings Are Great! Leno's Ratings Are Also Terrible

From an NBC press release: NBC’s “The Tonight Show with Jay Leno” has won the week of August 30-September 3 in adults 18-49 and total viewers over all cable and broadcast competition, delivering bigger audiences than CBS’s “Late Show with David Letterman” and ABC’s combination of “Nightline” and “Jimmy Kimmel Live” in every key ratings category: adults, men and women 18-34, 18-49 and 25-54, as well as total viewers. Note that “Kimmel” was in rebroadcast last week.
Jay generated his biggest 18-49 audience in eight weeks (since the week of July 5-9), his biggest overall audience in five weeks (since July 26-30) and his biggest adult 18-34 audience [...]