Your article only rates recruiting classes, not retention. In fact, if you want to point the finger at Riley for not retaining all of his higher-ranked recruits, then you have to also acknowledge the large number of high-rated recruits that Pelini did not retain. There have been multiple threads on this in the recruiting forum.
@Mavric did some research on this subject as well. Riley's recruiting wasn't significantly better or worse than Pelini's overall. Pelini's last two classes were a little below average, though.