The reason we're seeing Supers start to jump in greater numbers is because Obama appears to be pulling away. (And I say this as someone who will happily pull the lever for either candidate in the fall.)

Hillary's campaign appears to be in real trouble. Obama now has a double digit lead in the Gallup Daily Tracking Poll, the first time we've see that kind of spread. Obama was badly hurt by Wright but quickly recovered, while Sniper-gate continues to drag Hillary down. Her negatives are now significantly higher than either Obama or McCain, and continue to grow, which runs counter to the theory that she's thoroughly vetted. And now there's word that her campaign is starting to walk away from it's bills, which suggests finances are a good deal tighter than Clinton has let on. Put all of this together and you don't get a very encouraging picture. And it's this picture, not some backroom 'fix,' that is causing Supers to throw their backing to Obama.