This is why he is hiding his tax returns until he absolutely has the nomination sewn up, or if he loses the nonination his wealth trough stays private.
Another reason Romney holds off, he is paying taxes at only 15% rate same as the hedge fund guys. This rate is for carried interest. No proof but lots of speculation that Romney is paying that rate. Would be conformed (or proved false) if Romney releases tax returns. More ammunition for Axelrod and the ignoramuses at occupy Wall Street crowd.... and for people who hate banksters in general.