It might have been like a giant game of chicken. Maybe everyone assumed that Hillary would get the dem nomination and so they didn't want to look like bad guys and start attacking Obama. When Obama DID get the nomination, well, they figured, someone of his limited experience will never beat McCain. When he "won", why then it's like...nuts...if we spill the beans there's going to be riots.
If the whole bc thing is true, I'm not sure what way it will go, but I'm not too optimistic that there's a whole lot of people left in power that care too much about the constitution.
Hence why I think Dean high-tailed.