why should the borders be smooth? this isn't civ 5 where provinces are all hexagons. real borders are ugly and jagged because they are generally based on some geographical identifier, like a mountain or *

* a river. just look at the IRL norway-sweden border; now there's a face a mother couldn't love.
speaking of rivers, PDS isn't "relying" on rivers to form a smooth border. they have provinces end at rivers for the sake of gameplay since in most games its hard to tell what province has modifiers like river crossing and such by looking at it, which is irritating and can be detrimental in multiplayer. it's a helpful simplification.
and regions?... really? have you even looked at the map? you can't even see the provinces for the regions! unless you zoom way in.