There's actually a gameplay reason why some people in the sport want to crack down on the grunting: players use the sound of the ball coming off the racket to determine characteristics of the shot.
http://www.time.com/time/arts/article/0,8599,1905782,00.html wrote:
The de facto head of the anti-grunting lobby, tennis legend Martina Navratilova, believes players of all rankings must have their throaty exclamations curtailed. She used her acceptance speech for the ITF's Philippe Chatrier Award — which honors dedication to the sport — on June 2 to say that grunting "is cheating, pure and simple. It is time for something to be done." Navratilova says grunting disguises the sound of the ball hitting the racquet, which she claims an opponent needs to hear to quickly gauge the power, spin and depth of an incoming shot.
There is some scientific evidence to support this claim. University of Sydney physicist Rod Cross has shown that a player's sensitivity to string tension decreases if they wear ear plugs or use a sound dampener on their strings — in other words, a tennis player's perception is dictated by aural stimuli as much as visual or tactile cues. Former World Number One and current Champions Series player Jim Courier notes that players face a similar challenge when battling under the flight path of noisy passenger jets at the U.S. Open's Flushing Meadows grounds. "It's tough for players to react to shots," he says on his Twitter page. "I don't claim malicious intent [by grunters] but the result is the same. It needs to be policed."