Actually the Artificial Turf being used is Toray Spuckturf, which was developed by Toray Industries way back in the 80s (or 70s?) and used for the WTA Indoor Tokyo event for years before it moved outdoors in 2006 (7?). Hingis and Davenport loved it obviously.
Today I'm pretty sure that it's laid over a special matting. Go here: http://www.toray.com/ir/pdf/lib/lib_a004.pdf
and do a search/find on the word Spuckturf. You will see the kind of technology I'm talking about. And this is from 1999!
Like Taraflex of Gerflor, which is a pvc surface, the carpets of today are perforated to provide some resistance to control the pace and heighten the bounce some.
This Spuckturf would be laid over this perforated foam mat to soften the surface (slower pace) and if there were some ridges and the carpet loose laid it would also create bounce.
This summer I played on an outdoor artificial turf laid on concrete. Surprisingly it wasn't as fast as one would expect. There was sand strewn across it (near beach) which helped slow the pace and create some bounce. Plus, the concrete base was far from level at that time, so depending on where the ball hit, it could actually bounce up quite high, or stay real low. Nadal and Djokovic would have loved it! Haha! Babies
Anyway, that's another thing I was wondering, if there was any sand or rubber granules put on the surface. I couldn't get my hands on any HD Pics or high quality stream to tell. That would also slow it down.
At times it has looked really fast. Other times there has been a lot of rallying for a carpet surface with today's racquets and man power.
Lastly, the ball could effect it greatly. As far as I know it's a Dunlop Fort All Court , which is fast. So that wouldnt be it. BUT, possibly it's a Dunlop Fort Elite or even heavier slower ball.
From the little I can tell, it's what's underneath the Carpet that's slowing it down a bit. Not the ball or top surface. Still, in the end, very fast for today's power tennis.
NONE OF THIS EXPLAINS THE RIDICULOUSNESS OF PLAYING THE SEMIS AT THE SAME TIME! Economically it makes no sense to me. There must be a reason, logistically, that they did this.