I won't say it's true that he improved while Addai declined. There are only three years of stats for both guys. 2006-2007 Maroney improved ypc from 4.0 to 4.8, but that's expected with arrival of Moss-Welker and spread formation. (His 2008 ypc was 3.3 in limited action of 4 games.). Contrary to showing improvement, actually Maroney's averages declined in 2nd half of 2007 but then he had 100yd games against Jets and Fins in last 3 weeks raising his average. 50% of Maroney's career yards came in 2007, which should tip ypc in his favor. Another thing - Maroney was a pass catcher in his rockie year but seldomly in 2007 or afterwards. I put the numbers below but feel free to check the source NFL.com's Maroney stats
Laurence Maroney: Game Logs.
Addai's numbers were incorrect. Here are correct 3-yr stats from NFL.com:
Last 3 seasons (2006, 2007, 2008):
Addai:
Carries / Yards / TDs
642 / 2697 / 27
Maroney:
Carries / Yards / TDs
388 / 1673 / 12 (Note: 185 carries/ 835yds from 2007 was assisted greatly by the PERFECT PASSING OFFENSE)
Receiptions / yards
Addai 106 / 895
Maroney 26 / 310 (receiptions by year 2006/2007/2008: 22/4/0 - he was abandoned from screen plays from 2007 forward)