Those precautions do not mean that only conservatives do it or that only liberals answer the phone. What does removing the HERMIT vote do to the poll results? :^)
There are lots of people who just don't respond to these calls. More and more are depending on cell phones only, and those are not even called in these polls.
This is the best explanation of the Gallup results:
http://www.freerepublic.com/focus/news/1803763/posts?page=35#35