Also, when you mean "actual smoothing", I assume that is when you go into Mesh > Smooth [] ? ...
Yep!
Clearly I am a Maya newbie but is this what you essentially end up doing for the final render view for all polygonal objects?
Yes, typically smoothing(there are a few ways) is done when the model is ready to be rendered, as smoothing/undoing can be clumsy and even a little risky.
NURBS works in a similar fashion too I assume right?
Yes and no. Yes, because they both can be setup to be subdivided at render time to desired levels. And no, because they are constructed differently there is no "smooth NURBS" operation you can just run to add resolution like you would a polygonal surface.