The plumber doesn't have to do anything. He won't even fix your plumbing if he doesn't charge you. He is there to fix the plumbing however, no more or less. Any collateral damage to walls, ceilings or floors that is required for access to repair is your responsibility to repair it.
Unless you prefer to pay plumbers for drywall repair. Don't think you have to carry one of those large 4′ x 8′ plywood sheets just to make simple drywall repairs. As for your question, yes, plumbers have to cut walls all the time to get to the pipes inside the wall. Generally speaking, the plumber or electrician will open the wall to make whatever repairs are necessary and leave the patch to the property owner to repair or replace the drywall when finished.
The short answer is that you probably don't want an electrician or plumber to fix a hole in your wall, it's not their specialty. These service providers are your best bet for patching drywall or drywall holes that plumbers, electricians, and other service providers can create while working. My experience is that most plumbers and electricians who have earned top marks from Angie's List members don't include this type of repair work in their offerings. It's not unusual to have some stubborn holes in the wall after a plumber fixes a leaking pipe or having an electrician rewire.