I think there are two principal reasons for Obama's omission of military service from the commencement address. First, in the guise of praising public service, Obama sings a song of himself. His work as a "community organizer" in Chicago is more praiseworthy, in Obama's eyes, than work for profit-making companies in the private sector.
George W. Bush on Sunday, approaching genius. Note that he spends 81 words discussing military service (most of which are spent congratulating people receiving their commissions), 88 discussing private sector work (most of which are spent talking about the need for greater responsibility and ethics) and several hundred talking about the dread "public service". This is out of 2700 words.
I eagerly await their repulsion at his anti-capitalist pacifism.