I have never agreed with this idea. Both Gore and Kerry were, and are, awkward, unattractive, spoiled, lefty, loons, the endless fraudulent puffery both received from the ratmedia notwithstanding. The crucial difference this time around was Bush and Rove's four-year, grassroots vote building effort, particularly in targeted states such as Ohio and Florida. Bush and Rove's plan and its execution worked very well. That is the big difference between 2000 and 2004.
I have a theory that, at least on the Democratic side, it matters less who the Presidential candidate actually is. The Democratic turnout machine will "switch on" for anyone as long as the requisite pile of money is available.
Furthermore, I think that base Democratic voters simply don't care as much as Republicans who is representing their Party. So much of the appeal is grounded in a hatred and distrust of Republicans that it just doesn't matter anymore. It's almost as if Democrats are practicing parliamentary government, where you vote for the party and not the man.
So Democrats will accept poor campaigning, poor communication, lies, randy sexual behavior (Bill Clinton) and even outright illegal activities (Bill Clinton) that would sink a Republican with his base.
And Kerry got 57 million votes, the second most in history.