A memory mapped API isn't inherently more (or less) subject to compatibility issues and versions than any other kind of API. With the C-64 it was hard-wired but

A memory mapped API isn't inherently more (or less) subject to compatibility issues and versions than any other kind of API. With the C-64 it was hard-wired but that's not any more necessary than burning the OS on to ROM. (Which is to say: totally necessary at the time, for a machine of that capability and cost, but not at all necessary for systems that have the APIs we're comparing it to.