Maybe mostly liberals go to the CNN website in the first place? Personally I almost never go there, and never participated in their polls.
Speaking of which, it will be interesting to see polls come out after the selection of Sarah Palin. If they are bad news for McCain/Palin, it will be all over the news. If we don’t hear any polls, however, that probably means good news since they won’t want to publicize good news for this ticket.
The first poll has already been issued by Rasmussen. Palin got very positive reviews, including 63% from unaffiliated voters.