The house I purchased is the first time I've ever even seen access to shower pipes. I've got an access panel in my closet to a space above the garage that has access to the ones for the guest bath. I'm pretty sure it's not intentional either since the space goes to the master bath as well yet the shower is set up in a way that doesn't have access.

In my experience you usually have to tear out parts of a wall to access shower/tub plumbing. Definitely seems dumb now that someone pointed it out.