You think they asked the question differently for Palin than for the other candidates? Why do you think that? Have you seen the questions?
I think they asked the same questions. I'd question how representative their respondent pool is of conservative Republicans. People with a liberal bent are going to find more to like in Mitt or Huck than in Sarah. I suspect with some practice you can tune your respondent selection methodology to areas where you're more likely to find those people, and I wouldn't trust CNN not to do it.