You also have to consider that there may be some folks who live in some areas who, if you ask them, would say "I'm independent but tend to vote republican". These people are really republicans, but don't want to admit it because of a stigma that is out there in some places. I believe this has most to do with class issues. On the other hand, I'm sure there are many out there who say they are democrats, but will often vote republican for the same reason.
Well, the point is that you can't call a poll accurate, if the sample is way out of proportion with reality. The liberal press wants to wail about 'polarization of politics,' 'a country divided politically' but then they print polls as if nobody really cares. It doesn't add up.