What a difference a couple of months makes, right?
Before I return to the Gang of Four, consider the absurdity of Nadal-slayer Rosol falling 3 spots after Wimbledon to 103.
Let's look at the Gang of Four and compare their points through Wimbledon to what they were at the end of last year.
Federer 11,075 (up 2,905 from 8,170)
Djokovic 11,000 (down 2,630 from 13,630)
Nadal 8,905 (down 690 from 9,595)
Murray 7,460 (up 80 from 7,380)
I thought it was going to be a daunting task for Djokovic to defend all those points, and I was right. Nearly half of the points he lost came from 'only' making the semis at Wimbledon (down 1,280). 640 came from losing to Isner at Indian Wells, 390 from Clay season, and 320 from Dubai. At this point last year, he had 8 titles; now he has 2 (1 slam and 1 master's).
The obvious thing to point to for Federer is winning Wimbledon (accounting for a gain of 1,640 points). The next ones are him winning Indian Wells and Madrid (a gain of 1,280 points, I believe). But if he hadn't won Dubai or Rotterdam (up 640, I think) or played Halle, then he wouldn't be #1. He's lost some points by not going as far in Miami or at the French Open, but the stretch he's gone on has been incredibly good. At this point last year, he had 1 title; this year he has 5 (including 1 slam and 2 master's).
Counterintuitively, Nadal had 3 titles at this point last year, but 4 this year (1 slam, 2 master's). His final winning percentage is 80% this year, where it was 30% last year. What gives? Going from runner-up in a Slam to out in the second round inflicts great harm on your ranking points. The blue clay experiment didn't help either (another 510 points lost), and going from runner-up at Indian Wells and Miami to a semi-finalist hurts too (480 points lost).
At this point last year, Murray had 1 title (Queen's) while he has 1 this year (Brisbane). He didn't have as terrible a letdown after the Australian Open as he did last year (final at Miami), which probably accounts for gaining points, even with a less impressive clay court season than last year.