We call it MicroEMACS to emphasize the fact that most of the commands are very similar to, if not identical to, fundamental mode EMACS commands (actually, it implements a set of rebindings used by a group of users at Digital).
We call it MicroEMACS to emphasize the fact that it is but a shadow of full EMACS. No attempt has been made to make MicroEMACS wildly customizable (without writing code), or to have extensive online documentation. All of this sophistication was thrown away right at the start, because it was important that MicroEMACS run on little computers. In all fairness, is should be stated here and now that the most popular small computer these days is the MicroVAX!