What is the difference between the GOP and the Dems?

It seems today that there is one main divide among the two major political parties in America. The Republicans are for the haves and the Democrats are for the less fortunate. This seems to me a good vs. evil. Why then have the dems only held the white house 3 times in the last 10 elections? Is it that America has lost focus on it's values, or does it prove how selfish americans really are?