If you watch "The Unbelievable" DVD, Ronnie was 287-lb there, and was clearly in contest condition. I think Ronnie was so far ahead of his time, that neither he nor Chad realized that he could have come into contest at 287-lb, hence the weight drop. In 2003, they basically realized that Ronnie could easily be over 280 in contest, and decided to actually come in at 287. But Ronnie had that size in 2000. It's not like he gained new muscle in 2003 - it's that he actually decided to not cut the weight coming into the contest. More evidence of this is Ronnie in the 2002 Battle for the Olympia DVD. He was something like 275-lb in that video, and clearly in contest shape. Yet he decided to drop 30-lb and came into contest WAY underweight. Had Cutler competed that year, I believe he would have won, at least if he reproduced the physique that he showed at the 2001 Mr. Olympia contest where he placed 2nd. It's sort of sad that Jay decided to take 2002 off, in light of Ronnie's lackluster [for Ronnie's standards] performance.
In 2004, based on his size at the press conference to his size on the stage, I have one word:
over-diuresis.