PPrune Fan #1 is quite wrong, the rotor and transmission are not taxed by turning under no load. The overhauls on these components is not affected by ground runs and taxi-ing on the ground.
212man is right, crew times would be affected negatively (fewer real flight hours per month) but that is not the big driver, because the customer would have to pay the entire operation more money to carry the same pax on the same trip. More money, more business.
I know these facts cold, when I worked for a helo airframer, we were constantly asked by operators to make ground and taxi time part of the overhaul TBO, so that these operators could charge the oil companies for that time, too. IFR holds would (will) become money making revenue time, time turning in the chocks rings the cash register.
I know of one North Sea operator who refused to increase the cruise speed of his helicopters to match their performance, because he could bill more hours for the trips he flew!