You're fooling yourself if you think Maya isn't adding polygons when you toggle Smooth Mesh preview. Quick way to show yourself is: 1: Add a box. 2. Ensure Display > Heads Up Display > Poly Count (or whatever it is now) is turned on. This shows verts, edges, faces counts in the viewport. First row is total counts, middle row is for selected objects. 3. Toggle Smooth Mesh Preview and watch the numbers change.