You must have missed the Marist poll posted here the other day. The number was much higher than that. If I remember correctly 28% of respondents said they would be unlikely to vote for a woman in 2008 regardless of whether she was a Democrat or Republican.
I think the challenge is to find a Margaret Thatcher. Right now neither party has one.
P.S. I think it was a Marist poll but it might have been Gallup. Posted sometime in the last couple weeks.
Alas, I fear that you are correct. Give us a Lady Thatcher and I will vote for a woman every time.