For the believer, theoretically, God created both nature and the Bible. The accounts in each clearly contradict each other (for a Biblical literalist, at least). So, what reason is there to claim that nature is the deceptive side, and the Bible true? Isn't it just as likely that the account contained in nature is true, and God is deceiving us in the Bible? From a logical standpoint, I don't see a reason to pick one over the other.
Obviously, the rest of the religion is built around the Bible, so that provides psychological motivation to protect that side. But I don't think I ever realized how arbitrary their choice seems on logical grounds, even putting aside the other problems with the idea (verifiability, Last Thursdayism, etc).