Perhaps the usage of commencement is to refer to the beginning of a new stage of ones life after the years spent learning and then forgetting much of what was taught for all those years after kindergarten. That reminds me of a poem or song i once learned:
Plato, Euripides, Socrates, Diogenes,
Were known for their Philosophy.
The more you study, the more you know,
The more you know, the more you forget,
The more you forget, the less you know,
So, why study?