The choice of a commencement speaker in American Universities is based quite frequently on worldly accomplishments, rather than being based solely on formal, university-centric, accomplishments. It is as it should be: Even the purpose of formal education is to assist the graduates in helping the world along anyway.
Years ago, we heard Steve Jobs giving a moving commencement speech for Stanford students in 2005. The latest example in 2012: Nipun Mehta, Founder Of Service Space, Delivers Inspiring Graduation Speech To Students At The University Of Pennsylvania. Neither of these have earned PhDs, but both have exhibited a lot of unconventional thinking.
Some additional googling takes us to an interesting TEDx talk by Nipun Mehta on YouTube: TEDxBerkeley - Nipun Mehta - Designing For Generosity.
If you, as a reader, is a recent graduate, I hope this blog post will help you derive inspiration from these two.