I'm getting to be a broken record on FR but.....for Obama to say to the super PAC in question (which is not his, but does obviously support him) to return Maher's donation would be a violation of campaign finance laws.
You are absolutely correct ... however:
At the press conference, Obama recognized, but refused to answer, a question about liberal commentators’ language, and also The Daily Caller’s impromptu question about Maher’s language.
“Should Bill Maher apologize for what he said about Republicans?” TheDC asked.
Obama responded by saying “Thank you.”
Source: http://dailycaller.com/2012/03/07/democrats-sign-bill-maher-for-fund-raiser-as-obama-urges-civility/
As far as I know there is no law to prevent the President from answering, oh say, "I hope that both Republicans and Democrats will keep the political discourse at a civil level." But he didn't ...
That may be true, but if someone who had given a million bucks to one of Romney's Super PACs said something similar, don't you think the MSM would be screaming about Romney returning the money, whether or not he could do it legally?