Politicians don't say things "innocently"
I've watched a few re-runs of the speech and I'm quite certain the remark was "planted".

The audiance reacted to the word "lipstick" and Obama looked oh so slightly startled, as if he didn't know what they were laughing at ...feined innocence??. However, just for a second, a slight smirk passed across his face, just enough to let them see that he knows what they know!
Writing in todays Sunday Times, radical feminist Camille Paglia says of Mrs Palin...."It is premature to predict how the Palin Saga will go. I may not agree a lot with her about basic principles, but I have immensely enjoyed Palin's boffo performances at her debut.
A feminist that cannotadmire the bravura under high pressure of the first woman governor of a frontier state, Isn't worth a bucket of warm spit"..............I'll second that opinion......Ake

Camille Paglia's articlHEREe