Hillary could just as easily be characterized as the velcro woman to which everything sticks--albeit unfairly -- bringing her negatives to extremely high levels. I'd rather take my chances with the guy who thus far has been able to avoid any major damage from campaign flare ups.
Obama did not call Pennsylvanians bitter. He suggested that it is not surprising that a certain subset of Pennsyvanians are bitter that their jobs have all gone away-- a statement that is completely true. If Clinton made such a comment she would not have to worry about being forced out of the race.
Also, if you think the media is so biased against Clinton in the primary, what makes you think things would be any different if she were to go up against the Republican media darling, John McCain?