I've often read that the pros play the game -- probably esp. so at majors -- backwards. That is, they look at what the green (and the green complex) has to offer (pin position, slope, receptiveness to irons, where not to be if you hit a bad shot), and work back from there. Based on my viewing so far, it seems like most of the guys near the leaderboard (esp. true w/ Tiger, but I really noticed it with Donald yesterday), these guys know that nearly any iron will stop on these greens, and -- working backwards from there -- are focused mainly on the tee on hitting the fairway and putting it in the proper position off the fairway. Donald hit a lot of non-drivers off the tee, for a guy who's not very long, but left himself with a lot of putts in the 10-25 foot range because he knew most any iron he hit into the green would hold. Thus, player's comments that the course "isn't playing that long," because they are able to hit a lot of non-drivers off the tee and still have good shots are birdies.
That, to me, seems like the key difference in the set-up between Medinah and WF at the US Open. WF was just as long as Medinah, but tougher green complexes, more severely sloped greens, and -- if I recall -- somewhat firmer/faster playing conditions brought more risk into a player's decision off the tee. At WF, there seem to be a real difference attacking those greens w/ 9-iron vs. 6-iron. At Medinah, it doesn't seem to be that big a difference.