My thoughts on why Senator Clinton should concede the nomination: A Senator Obama, stung by a stolen presidential nomination, would outshine a President Hillary Clinton. And if Hillary Clinton were to lose the presidency to McCain it would mark the end of the Clinton era.
Basically, she cannot fairly win the Democratic presidential nomination at this point. But she delusionally thinks Obama cannot win (See: Richardson endorsement still irks Bill Clinton: Meantime, Hillary reportedly told Richardson that Obama can't win). I cannot imagine Obama ever saying this about Clinton.