brake pad change is actually called brake service. when they are changed the discs are inspected for weardown and are changed if under manufacturer specification, rubber parts are changed out if worn down too (the workshop is held liable in case of any accident caused by such worn down parts left installed on vehicles they service)
drum brake service is quite simple and easy. Its just a simple wash down with soap and water, then a few dabs of greasing and a bit of adjustment - Shops just charge ONE wheel charges to service two wheels of drum brakes - unless springs and hardware is being swapped out - and this is done when the car rolls in for a brake service job (pad change etc).
The one very vital bit of brake service is flushing out the brake fluid. A very critical and necessary job.