John Sides nods:
[H]ere is the problem that Romney confronts. Americans perceive him as personally wealthy more than they do Obama. They perceive him as caring more about the wealthy, but less about "people like me" and the middle class, than does Obama. Moreover, Obama can "get away with" being perceived as personally wealthy or caring about the wealthy in ways that Romney cannot. For Americans, Romney’s personal wealth is more intimately tied to the perception that he cares about the wealthy—and this in turn implies that he cares less for the middle class.
Similarly, Frum points out that America doesn't typically elect the super rich:
Before the Civil War, the parties (and especially the Democratic-Republicans) often nominated presidential candidates wealthy in land and slaves. George Washington, Thomas Jefferson, James Madison, Andrew Jackson, and John Tyler were some of the richest men of the young Republic. But since 1865, it has become unusual for parties to nominate very wealthy men. I can think of only five very rich post-1865 presidential nominees: John McCain, John Kerry, John F. Kennedy, Herbert Hoover and Samuel Tilden.
The Dish 