HYPERBOLE OR BS?

The buzz in the press about Clinton & Obama is that her supporters must come over to him or he loses. Here's an example from ABC's The Note:

If Clinton supporters don't come to Obama's side in greater (near-unanimous) numbers, he loses the presidency.

If this were true, then why do the polls show Obama with a lead over McCain? The RCP average for today shows Obama leading, 45.7% to 44%. Are many of the Clinton supporters waiting to see how the DNC Convention goes and then, perhaps, going to change to supporting McCain? If so, where's the evidence?