Additionally, the Romney campaign has come close to denying speculation that Romney paid no taxes whatsoever.
So -- grain of salt.
But without suggesting that Romney deserves these sorts of attacks, or is getting what's coming, he's going to be hard pressed to demand retractions and circumspection from people in Reid's position. By refusing to release more returns, he's created an incentive for senior Democrats to lob incendiary accusations into the public sphere. Even if they're totally baseless, it ratchets up the pressure on him to prove they're false. But he can't do that without releasing the very information he's consistently refused to release.
How do you disprove that you didn't pay any taxes for 10 years? You release 10 years of tax returns. By sheer coincidence I'm sure, that's exactly what Democrats want Mitt to release anyhow.