[networked]

Or c) a person applying at the last moment has enough confidence in his or her product that applying to YC seems optional rather than urgent.

That said, it would be strange if all the people who applied at the last moment, even all the successful YC alumni who did, did so for the same primary reason. I'd wager that it's more that there's a cluster of desirable founder traits that correlates with applying late, of which in any particular good founder a different one can dominate.