Re: Does this equate to "yes, there's depth on the WTA tour"?
This is my theory on the differences in depth between the ATP and WTA.
On the ATP, all the men are (relatively) equal skillwise. Anyone in the top 100 is capable of hitting good shots, good serves, etc. The biggest difference between the top ten and everyone else is mental- the top ten chokes, tanks, etc. less than the rest. Take someone like James Blake. A top fifty player, who makes a comeback, gets his mind and tactics in order, and become four in the world. Or Fernando Gonzalez. A guy who couldn't hit inside the lines before makes it to the AO finals.
Even in the top 3 this is evidence. In the USO final, Djokovic was outplaying Fed for a lot of the match. He just choked on the big points.
On the WTA, even the top women are prone to lapses. So the main difference between the top ten and every other player is skill- the top five women are simply better than the rest, and they win- easily- over lower ranked opponents.
So, logically speaking, it's easier for a ATP to have a "good day" than it is for a WTA player to obtain skills she's never had before, which is why the top female players almost always win.