One confounding variable here might be the fact that conservatives are actually less likely to use Google. There has been a strong backlash that I've seen personally, where conservative members of my family actively encourage me to stop using Google because it's in some way "liberally biased" and that it has a "hidden political agenda" and is trying to "impose its radical views on the world." I'm not making this up, there are even books on this very subject. One example is "Search and Destroy."

Google has an advantage in mindshare in that it's effectively the "default" search engine on the web, but its population is still, to a degree, self-selecting. Whether this effect is pronounced enough to skew the data, I can't say.