Phil:
The grasses in the fairways at US Open courses are generally bent, and the rough grasses are rye, fescue, or bluegrass, or some combination. It is a very expensive proposition to strip out the rough grass and plant and establish bent after the tournament is over. Therefore the fairawy widths tend to remain, though the rough is obviously cut lower.
THe 18th at Torrey will be a par five and the grass around the pond will be shaved, which will make the risk/reward choice interesting (though I'm not real keen on the idea of the shaved bank, personally.) It's a good bet that the fountain/circulator will be turned off during the competition.
One of the set up decisions under consideration, as has been reproted in the golf press, is to have the primary rough be thinner, though still in the 5-6 inch range.