Fox was CC'89.
Easily the best speaker in recent years was Tony Kushner (CC '78) Speech here: http://www.college.columbia.edu/cct/jul04/cover.php
The dirty secret is that people don't want to speak at class day. Columbia University's University Commencement address (delivered before a crowd of 50,000) is an honor the President keeps for himself. One of the few times that didn't happen was in '68 when Grayson Kirk was on the way out thanks to the protests and police busts in april. Historian and professor Richard Hofstadter spoke instead.
Class day, the College's individual ceremony attended by about 4k to 5k, is when a guest addresses the students. A much less compelling offer.
In 2004, Kushner was the 4th choice. Rumor has it that Fox was far lower on the list. Far, far lower.
And I'd be shocked if Obama speaks at CU anytime soon. The man barely acknowledges having attended the school. He'll be addressing Harvard's graduating class next year though most likely.