Actually, if you check the stats...
1. Clarett's production in 2002 > Pittman's production in 2006.
2. Lydell Ross' production in 2002 > Beanie's production in 2006.
3. Maurice Hall's production in 2002 > Mo Wells' production in 2006.
4. Krenzel's rushing yardage total in 2002 > Troy Smith's rushing yardage total in 2006.
The 4 above from 02 outgained the 4 above from 06 by 400+ yards & 8 TDs. Clarett wore defenses down from the start, while Beanie had the luxury of running against tired defenses when he was put in. If anything, Beanie had the bigger benefit of timing. He played a few games with a messed up ankle, and Clarett played a few while suffering from a stinger. The 02 Bucks also beat a team that was better than the one that the 06 Bucks eventually lost big to.
Stats from both years can be found by clicking on the links below.
2002
Football Statistics
2006
Football Statistics