This is a silly poll, as it assumes that it is unimportant who would be running against Obama.
If you restate it as Huckabee vs. Obama, Romney vs. Obama, Palin vs. Obama, Gingrich vs. Obama, each would give different results.
If Obama did receive 50% of the vote, he would win, because there are always some third party candidates that would result in Obama's opponent getting less than 50%.
But I was not expecting adequate mathematics skills.