I respectfully decline to agree
(after reading the post)
They are both designed to turn larger things into smaller things. The overwhelming majority of pepper grinders appear to be simple/cheap burr sets. Not much marketing seems to go into claiming any unique pepper technology. Perhaps there is a difference? If so... the world of artisanal pepper lags behind the world of artisanal coffee! But the subtleties are not obvious or convincing to me.
Surely the major parameter is that using freshly ground pepper produces richer aromatics than stale, preground stuff. I am happy to agree that there is a texture/consistency difference between pepper grinders and a mortar and pestle. I am also happy to agree that texture and grind size makes a difference to taste and experience. Beyond this.... isn't all the rest over optimisation and preference?
One noteworthy point of difference for milling pepper vs other spice is whether the burr will corrode if you put salt into it.