Nobody ever said exactly why Humphries decommitted, but an Indy Star (sorry, unable to link to- article purged from internet) article speculated:
"It's unclear why Humphries asked out of his Duke commitment, but speculation has centered on the possibility that Duke coach Mike Krzyzewski was not happy with rumors that one of his recruits might be leaning toward leaving for the NBA after just one or two years of college. It's believed that Krzyzewski traveled to Minnesota to speak with Humphries about that topic.
Another possibility mentioned is that Humphries realized there was a glut of big men at his position at Duke.
When asked why his son asked out of his letter of intent at Duke, William Humphries said "there's a legitimate reason" and added that the information would come out in the appeals process."
Here is an editorial from a Minnesota newspaper on the decommit.
