Aaron Blake does the breakdown:
...Romney won this demographic by 14 points but didn’t win among any other income demographic. And given he won by such small margins overall — 1 point in Ohio and 3 points in Michigan — it’s not unreasonable to think he would have lost those states without the uptick in wealthy voters.As Blake mentions, wealthy Republican voters increased by almost 50% in Michigan this year as well. The rich are protecting their own. This would be class warfare if it happened on the Democratic side.