Those game were an improvement on the same formula, yes, but offered almost nothing new at all. and how is SMB2 a bad example? I LOVED that game- I played it for hours on end when I was little, and sometimes still pop it into my NES to give it a whirl. One of the best platformers ever, if you ask me, and I'm sure many here agree with me. It really didn't change the Mario formula, either, just the appearance.
Cubed: What a productive comment!