I may be biased, but I don't think his game has been that physical...his strength in his prime was to take the ball early and control the rallies with his FH, moving the opponent from side to side and attack. Although his primary strength shone on clay, his tennis has been adoptable for fast surfaces as well (He started playing tennis on hard courts as a child). His serve has never been massive, but he has a very reliable kick second serve that has won him many points (In 2003, he was No. 1 on the second serve points won table on the ATP stats, and No.2 on first serve points won after Roddick). Unlike some players whose main weapon is their FH, his BH is no liability either.
Anyway, 2004 was annus horribilis for him....the first sign of physical trouble started during AO where he had a back and abductor problems, the latter of which hampered his movement during SF against Federer (Ferrero's both thighs were heavily taped.) Then chicken pox hit in March, followed by a minor wrist injury and a rib injury just a few weeks before Roland Garros where he was the defending champion.
I think all those problems stemmed from too much tennis in 2003. Reaching two slam finals and winning one, playing his third Tennis Masters Cup, and reaching the Davis Cup final in which he lost to Hewitt and Philippousis in five sets on Australian grass in December.
And I think he made mistakes by returning to court too early after the illness and then after the rib injury, which I suspect was a main reason for his FH becoming less potent than it once was. Apparently his coach and entourage all told him to withdraw from RG that year, but he insisted on playing. Anybody who watched him play that year would know that he was in no shape for playing competitive tennis and that it was a near miracle that he won the first round against Haas. Ferrero couldn't even raise his arm properly to serve.
Then he changed his racket from Prince to Head in the autumn of 2004, and IMHO that was not the right time to make such a change because I think he still hadn't fully recovered from the injuries, which also affected his footwork. (He officially returned to Prince in 2007)
Some signs of his return to form could be seen from 2006, and I think he has been slowly getting back to where he once was. Sure he's not getting any younger, and he might not have fully regained confidence, but he was actually playing some good tennis in 2008 although another abductor injury hit him in April and sidelined him for three months from June.
I just hope he will have an injury free season this year, and, if possible, that he will be able to win a title again....
Also, I remember him saying he didn't feel like a "real" #1 being there only for a short while. Prolly found it difficult to have that same motivation after scaling the rankings and then to peak there for a short while.
When and where did he say that? I don't think I've read/heard that kind of remarks by him.