They are similar in some basic respects, but it would be like saying a chainsaw is just a steak knife with more options.
Micromesh replaces every polygon in a subtool with a selected mesh. Nanomesh lets you apply an instance of an object, or a combination of objects, to any selection of polygons you designate, without replacing the underlying polygons. The nanomesh menu provides a wealth of options for positioning, sizing, and randomization. You can edit the original object(s) at any time, and see the changes updated in the applied nanos. This has all sorts of different applications, from quickly constructing or embellishing buildings, as I have done, to placing randomized elements through a scene, like tree leaves, or quickly creating organic textures for objects like trees or rock walls.


