Only three setters from QF in Aus Open '08 and US Open '07

I noticed that there were only 3-set matches from the Quarterfinals on in the men's US Open 2007 last year. That pattern has continued in the Australian Open 2008 (at least through the semi-final round).

Here's a graph:



I began to wonder what's going on here. It's as if when the QF arrive, the 4- and 5- set matches just vanish. There are fewer matches, so it's possible it's just variation on a normal curve, but BOTH tournaments?

It's not just that more of the matches include guys named Federer and Nadal, who are taking everyone out in three, though at least that could be partly the cause with Federer. This Australian Open, however, both those guys lost in straight sets in the SF round.

Is it just that the initial rounds are more competitive, with guys ranked between 30 and 80 just duking it out to more? Maybe, but often the top players are involved in the longer sets in initial rounds too. They just generally have the ability to come back from it, perhaps aided by less experienced players choking once they get a set or two.

Is it because guys are getting weary as the tournament wears on and just can't mount a come-back? That may have more to do with it. I don't know the answer, but I'm curious about what others think. It is not true about Wimbledon 2007. Does it only work for hard-courts?

Links: US '07 QF | Aus '08 QF