This newscast from 2008 has Romney admitting that as far as he knows God hasn't spoken to anyone since Moses. He seems somewhat embarrassed to mention the First Vision. Former Stake President Romney is obviously aware that the entire LDS Church is based on the First Vision which has God speaking to the founder of Mormonism Joseph Smith. In short, Romney is a typical politician by not wanting to alienate voters by not appearing to believe in things most Christians would be very uncomfortable with.
Youtube video: Mitt Romney denies key tenet of his own faith!