Update Sept-16-2007 2:09PM: Pimpuk, my friend and tennis enthusiast weighs in with her observations:
"As you may have guessed, I watched Federer's matches on TV. I'm not sure if I can confirm or disconfirm the article said, but for me, it is quite accurate. But of course, it is subjective how one perceive what is going in a tennis match when the shots are going at around 100mph.
Though some may say that he does not bring his A game to all the matches like he used to during 2004 and 2005. But I guess that is understandable, he is human after all. And the question that comes after that is whether he needs to bring it at all.
Many times after his winning matches in which he didn't play that well, there will be comments that said "he did just enough to win". When his opponents didn't play that well, so why should he? He did just enough, focused during the time he needed to (for example, to break his opponent just one game per set). So I guess it can be said the "conservationist" aspect is accurate.
My friend and I (and, I think, quite a number of his fans) used to be afraid of the 2nd set of the match. Because after winning the 1st set, Federer seemed turn off, somehow. We used to say that he went into a nap in his mind, and then he pull himself back together just in time when it matters.
Same thing applies, I think, to what is said in the article. When Federer lost a set (to someone whom he shouldn't), he just came back stronger. I remember quite a number of times that after he lost the set, he won the next set and the match in such a commanding manner.
Another thing that, I think, the fans or viewers have come to expect is that he can turn it on when he needs to. For example, when facing breakpoint and his serves weren't doing so well, he can pull a couple of very good serves to escape, or during tie-break of the set.
Last but not least, I think "the conservationist" aspect of his game is not just about the mind. If you watch his game, you will see that his movements and manner on court are very economical. He never seems rush, but somehow manages to be in position for most of the time. No running back to the chair after a game, no sprinting to the back of the court, nor unnecessary actions that will require him to spend his energy more that he should.
Maybe I just over-analyzed everything, and he is just what he is :-)"