If you ask people to identify themselves as liberal, independent or conservative, you usually see a 20-40-40 breakdown. That would put the median voter somewhere around the center-right. I don't think there's much more to it than that.
What gets me though is if you look at labels, you are right. People tend to self identify as more conservative.
However, if you look at issues, people tend to be middle left overall, some issues they identify with the right though.
Ultimately, it makes me think that this is a matter of marketing over substance.
Examples:
http://abcnews.go.com/images/PollingUnit/1089a6HotButtonIssues.pdf <- a bunch of stuff
Civil Rights <- gay marriage (for)
Stem Cell Research <- stem cell research (for)
ABCNEWS.com : Poll: Stem-Cell Support Steady
TIME Poll: 61% of Americans Oppose 'Ground Zero Mosque' - TIME <- ground zero mosque (strongly against)
Daily Number: Future of the Bush Tax Cuts - Pew Research Center <- bush tax cuts again (I think this is a better quality survey than the polling report one) (neither side wins)
Americans Oppose Renewing U.S. Combat Operations in Iraq <- in favor of ending iraq war (even though this one is moot now)
http://www.pollingreport.com/guns.htm <- gun control (most prefer the current laws not be changed)
http://pewresearch.org/pubs/1535/poll-state-local-governments-laws-banning-sale-possession-handguns <-- gun control opinions heading rightward
http://www.gallup.com/poll/1576/abortion.aspx <-- abortion holding steady
The stimulus one is interesting, the opinion almost seems schizophrenic.
CNN Poll: 3 of 4 Americans say much of stimulus money wasted - CNN <- stimulus money seen as wasted
Americans Back More Stimulus Spending to Create Jobs <- americans back more stimulus
(I wasn't able to find anything good on general federal spending or taxation, I keep getting historical entries for poll taxes, I will try to think of a better search term if I get some time today.)
There are probably more social issues, but its early and my brain hasn't woken up yet.
The way I interpret this is while overall, the idea of conservatism seems good, when you get to specifics, people are slightly more liberal. Overall, the march towards a more liberal way of doing things in the social sector remains unabated because of this slight preference and that is why there are more and more fundamentalist conservatives as they seek to preserve what they know as good. Ultimately this is why there is preaching in the churches that America is going to hell in a handbasket and that we need to restore honor and what not. These people are (understandably, given their view on things) against the change that is slowly taking place from generation to generation. Ultimately, this is probably a reason people self identify as conservative, because of that change and the insecurity they feel in the face of it (with cries of, the world was so much better when I was younger!) Of course, that is all opinion and speculation and open to change as more data comes to light.