I'm listening to Roger Warren talk on The Golf Channel and I'm just blown away by how he's defending the maintenance of the golf course. He basically blamed the softness on humidity? WRONG. It was no more humid over the last week than it EVER IS in Chicago in August. In fact, it was much less humid.
Shiv,
My take was that it was hot all summer right up to the PGA week, when it unexpectedly cooled off. They were watering more, and then the grass slowed down its evapotranspiration, leaving them a bit damp. They may have dried out if not for that inch of rain the other night.
Also, factor in the history - Medinah has had green problems in most of the tournaments I recall, probably owing to the trees. I can recall them turning purple and being syringed in 75 and 90. I don't recall 99, but its possible they remembered that and overcorrected. Its still as much art and guess as it is science.
USGA greens are usually hardest the first few years, and gradually get softer. I think Tiger was wrong, Soft greens are usually caused by either a top layer of organic that keeps roots from penetrating deeply or a sand with roundish particles that never sets/firms up very well. If it was just excess moisture from rain or irrigation, a USGA green draining even on the slow end of 6-12" per hour would quickly drain those with proper sand.
I found myself wondering if they had a subair system, which could have sucked some excess moisture out if they drained slowly. Of course, they said Rees only rebuilt 7 greens, I think. Perhaps the rest are topsoil or other greens, and its even possible he built non-USGA greens to match the conditions of the ones not rebuilt, so they may have some drainage problems. I am guessing on that, but perhaps someone else knows?