Is there a reason why these two should be different?
I understand the numerical value is there in the simple .stl options because it is a reasonable gauge of what the export facet quality will be like if you’re not a meshing expert. The fewer-more polygon slider in the simple mesh dialog doesn’t really give that kind of assurance.
I’m throwing this out here because often we suggest that people mesh their objects in Rhino before exporting as .stl for 3D printing. The difference in the two dialogs when demoing this is disconcerting and hard to explain.