I guess McCain did too, when he used the same term to refer to Clinton's health care plan. It's just that Hillary didn't make such a production out of it.
Hilliary didn't use the word "lipstick" in any speech a week or two prior to McCain's use of the term. Did you miss Gov. Palin's speech at the convention? The "pit bull/lipstick" comment was one of the top 5 sound bites from her speech that was played repeatedly after the convention. If you watch the clip, the audience behind Obama knew what he was talking about.
That's one difference, true. Another difference, however, is context. No one took McCain to be calling Hillary a pig since she had not just called attention to her use of lipstick the week before. Is there any doubt that Obama's audience took him to be talking about Palin when they responded to his remarks with gales of laughter?