So why is the Obama campaign going for the jugular and critiquing Sarah Palin's experience? Shouldn't they be happy enough that the experience argument was essentially taken off the table by this selection?
Because it isn't really an argument about experience per se. It's an argument about whether she meets the basic threshold test of voters feeling comfortable with having her as President. Experience is a part of that, but so are essentially the aesthetics of it: picturing a young, attractive, kooky, female governor from Alaska who has an accent straight out of Fargo in the White House is going to be a much bigger leap for many voters than picturing Barack Obama there.
And whereas Obama has had eighteen months to make himself familiar to voters, the McCain campaign has barely any time to roll Palin out. It's not that she's inexperienced so much as that she's new.