Most US Launchers use a similar water suppression system for the same reasons as the Space shuttle.
At some level, if you intend to launch often you do not wish your launcher to destroy the launch pad. A rocket launching usually has between 600,000 lbs thrust (Delta 4's single RS-68) to 7 million lbs thrust (Space Shuttle, or Saturn V range) and that is an amazing amount of power released in a small space and it really does not matter what you build your launch pad out of, it will take damage.
Thus minimizing the damage caused is just a good idea, across the board. Water is cheap, easy to manage, and absorbs energy by converting steam, absorbs sound instead of the physical structure.
Russians for the Soyuz boosters have an interesting approach that does not use water suppression, since Baikanour is often experiencing winter when they wish to launch, when flowing water won't work so well (and snow is not as effective as water for this task). They basically suspend the booster over the edge of a cliff, so that the exhaust goes down, and then out a vent, such that there is not much infrastructure directly below it to be damaged.
Amusingly, the ASDS Barge that SpaceX is using for landing first stages has a deluge gun, to cool the deck during landing operations as well.