Why wouldn't Obama wait?

I love this section of Obama's stump speech where he talks about people asking him why he didn't wait to run.

"You're a young man," he says they tell him, adding that he responds by explaining to them what Dr. Martin Luther King Jr. used to call "the fierce urgency of now."

Obama takes twin swipes at Clinton as he explains that he does not see the presidency as something he feels is owed to him or the fulfillment of some long-held ambition (although he acknowledges that "people" (read: the Clinton camp) have been looking through his kindergarten papers and say otherwise, in reference to this incident back in December:

http://www.allheadlinenews.com/articles/7009344920

(Check out Bill Burton's response to the Clinton campaign, in the sixth graph. That is an instant classic.)

"There is such a thing as being too late," Obama says, "and that hour is almost upon us.

"We cannot wait."

Obama takes heat for being a great speaker who's short on substance. I don't know about the latter, but I can attest to the former. Policies completely aside, I just love listening to this guy speak.