Let me throw out some speculation on why half the people of in the USA dispute evolution. I think it's because of the conflict between the Young Earth Creationists vs. everyone else. (Am I correct in that this dispute and the push for Intelligent Design is rather stronger in the USA then elsewhere?)
They are being told by Creationists that you can't accept evolution and believe in God and Christianity. They perceive (and often rightly so) they are being told by
some evolutionists that they can't believe in evolution and God and / or Christianity.
See for example how this guy presented evolution vs. God to his mother and his frustration when she chose her belief in God. Until he put the question to her she was content believing both.
http://www.internationalskeptics.com/forums/showthread.php?t=105325
For the average person my guess is that they don't really care
how God created them. But if asked to choose one of these 1) Believe in God (and YEC) or 2) belief in evolution (and thus not God -
as they perceive it) they will pick the choice that adds the most meaning to their life. If they are even a tiny bit religious they'll choose 1, because what is 2 offering them?
They could believe
both - but is that even given as an option? Again - my guess is - apart from the thought of "Hmm ... evolution is interesting, but really, who cares if evolution is true - it doesn't help me put food on my table and pay the mortgage." It's probably not thought about much.