I think now you can define circles and extrusions parametrically. I'm sure I've seen videos of people adjusting circle radii and facet count and it adjusted the parameters and re-tesellated based on the new parameters. Visually you see the polygonal representation you asked for, but at least some things do seem to be parametric underneath if you define them in the proper way.

I also believe I read about parametric model definition being something they are working on more, since so many folks are asking for it. I do hope that comes to fruition. A free parametric modeler would be absolutely lovely.