I have no doubts that the media will make a big deal out of Romney's tax returns. First of all, he's been very successful and has made a good deal of money, so likely he will be slammed by the media. Additionally, because his overall income rate, consisting of mostly dividends and interest, is likely to be closer to 15%, so my guess is that the media will discriminate against him here as well.
But will the media look into depth into Barack Obama's Tax Returns as well - most notably charitable giving, where Obama gave almost nothing for many years. Only when he thought he might run for President did he start giving close to the American average. I doubt we'll hear much about this though.