First of all, it was the democratic party, not Obama, who refused to go on Fox. apparently the democrats were afraid Fox was going to sabotage their debates by allowing a McCain supporter to ask as ambush question. Just like the Hillary supporter who asked the question on gays in the military on the CNN debate.
Second, The New York Times (of all papers) said that the debates on Fox were more fair then the debates on CNN or MS NBC. Hillary Clinton practically admitted it when she openly questioned the fact that she was always asked the first question during the debates. Maybe she owes Fox an apology.
That's the problem with the democratic party, they're good when they preach to the choir, but they're afraid to play when they don't have the home field. If they can't face Fox News, how will they be on the world stage?