Why hasn't Edwards endorsed?

I figured Edwards was just holding back on his endorsement because this thing might actually go to a convention floor fight, in which case his 27 delegates might be pivotal. That would make him some sort of kingmaker.

But that's not the reason, says New York Magazine. The real reason is that he was leaning Obama, but Obama blew it:

According to a Democratic strategist unaligned with any campaign but with knowledge of the situation gleaned from all three camps, the answer is simple: Obama blew it. Speaking to Edwards on the day he exited the race, Obama came across as glib and aloof. His response to Edwards's imprecations that he make poverty a central part of his agenda was shallow, perfunctory, pat. Clinton, by contrast, engaged Edwards in a lengthy policy discussion. Her affect was solicitous and respectful. When Clinton met Edwards face-to-face in North Carolina ten days later, her approach continued to impress; she even made headway with Elizabeth. Whereas in his Edwards sit-down, Obama dug himself in deeper, getting into a fight with Elizabeth about health care, insisting that his plan is universal (a position she considers a crock), high-handedly criticizing Clinton's plan (and by extension Edwards's) for its insurance mandate.

That's actually pretty damning. One hears stories about how gracious and charming Hillary can be in a one-on-one meeting, even if that charm doesn't carry over during big speeches. Is Obama disadvantaged in the other direction? Is he great with the big crowds but clumsy in person?