Ok, so let's leave my opinion of Richt's abilities aside and focus on your statement:
After seeing the Rivals' rankings above, do you still maintain that UGA's talent has "fallen off"?
Using your threory, I can make a case that Pete Carroll is one of he biggest squanderers of talent there ever was. Only one undefeated season, and only one BCS Title. He did that in 2004 with a team that only had one 2 10 classes, and they were the underclassmen on the 2004 team. Between 2003 and 2009, he never had a class ranked below 5th, and had three ranked #1 from 04-06. He won exactly jack shit during that time after 2004, save some worthless Pac 10 titles, and in 2006 and 2007 could only manage a tie for the Pac 10 Title. 2009 was one of his more talented teams per Rivals, and they went 9-4/5-4 and placed 5th in the Pac 10.
However, both of the examples of Richt and Carroll, as well as Tubs support my theory of a coaches professional life at a big time BCS school being max of about 10 years. They just give out under the pressure of high performance being so dissapointing to the fans. They either quit coaching, or quit recruiting, or both.