It's the height of absurd to pontificate that Letterman would, ". . . give it to everyone equally."
It would be a rapid smack-down if he took even one of the satire opportunities that Obama has offered, and Letterman knows it. Any expectation that there is an equality in Letterman's "humor" is delusional.
Not a political strategist, but this appears to be giving Letterman the thing he craves -- attention. It seems it might have been better if Mrs. Palin had simply responded:
Letterman's writers often provide the show with tasteless or inane comments targeted for low-brow laughs. It is not worthwhile to ascribe any importance to what is said, or to attach any significance to such ramblings.
End of story. Case closed. Move along, nothing to see here.
What Sarah did was much more effective.
She deftly transferred the "knock up" joke to "Letterman is a dirty old pervert who lusts for 14 year old girls" when he stupidly didn't notice that it was Willow at the ball game not, Bristol.
Then he componded his idiocy by trying to explain that he was really talking about Bristol not Willow. And then inviting them onto his show.
Sarah then drove in the knife when she said "I won't let Willow go near that man". OUCH!!!
This is a shot across the bow of all liberals. This momma bear has fangs.