The actual finished edge is from the stone. The paste is just smoothing it out for a nicer shave, in my experience. Have a look under magnification after any finisher, then paste laps.

As far as the SG20K and justifying the cost, I had the same opinion too until I started reading more (and more) about naturals and their costs. I don't have one yet, as I went another route with BHs that I believe to be more cost effective. I still have it on my list. The BHs are doing a bang up job quite a bit beyond my 12K level.

Hope that sorts it out for you.