what good is letterman again?

david letterman apologists developed a healthy list of excuses, rationalizations and self-delusion to explain his nightly trouncing at the hands of jay leno.

even worse for letterman, the post-koppel changes at nightline shifted that shows viewing audience--namely growth in overall viewers and younger viewers.
the coup de grace is the aging of letterman's audience.

There's been a big shift in the median age of late-night viewers on the Big Three networks over the past five seasons, so much so that ABC’s “Nightline,” not CBS’s “Late Show with David Letterman,” is now the youngest of the bunch. So reports a new Magna Global U.S. study.[snip]
Meanwhile, Letterman has aged at a faster pace than any other show.
His median age has shot up from 46.5 in 2001-2002 to the current 51.0, a 10 percent increase. By comparison, “Nightline” is down 2 percent and “Tonight Show” up 6 percent in the same span.
[snip]
At its present pace, Letterman’s median age could outpace Leno’s by this time next year.

found via tv newser