WesDawg
'Burghapologist
Other RBs who fit this pattern :
Shaun Alexander had 5.1 in 2005, 3.6 in 2006, then 3.5 in 2007 and was finished as an NFL RB.
Edge had 4.6 in 2004, 4.2 in 2005, and then 3.4 in 2006. He never got over 4.0 again although he did have a decent season yardage wise in 07. It was the end of his relevence.
Warrick Dunn had 5.1 in 2005, 4.0 in 2006, and 3.2 in 2007. Although he still played in 08, he was total junk.
Ahman Green went from 5.3 in 2003 to 4.5 in 2004 to 3.3 in 2005 and never returned to elite status.
Marshall Faulk went from 5.3 in 2001 to 4.5 in 2002 to 3.9 in 2003 and became a fantasy football nobody.
These are the cases where YPC really matters. For those of you who are doubters I challenge you to find a RB who saw his YPC drop by 0.5 in 2 consecutive years who still found fantasy success following that drop.
I'll accept the challenge (sorta) and cite that all the guys you mentioned had either age issues, declining offensive lines/offensive situations, youngsters who eventually took their jobs, major injuries, new teams, or a combination of all 5.
And unless I'm really off-base here, neither of those guys' decline began when they were considered to be in their "prime". So again, taking the middle ground, possibly the YPC debate could be an indicator of when a formerly elite RB is exiting his productive time.