I agree; at UK or Miami he could take just six credit hours in the fall to maintain eligibility, then not take any classes in the spring. At Duke he technically could still do this, but I doubt the program would allow him to. Not trying to discount his academic integrity or anything, but I think this has to be a strong factor in his decision.
Regarding UK's title chances, they will have a ton of talent but also will be adapting to a new coach, integrating several blue-chip freshmen, and probably learning an entirely new offensive system. Also they will be jettisoning between two and four current scholarship players. Duke will have a more stable, veteran lineup.