It doesn't help that some laptops are 16:9 and some 16:10 so the vertical numbers get even more mushy. Anyway, my point was that even though "4K" as a concept

It doesn't help that some laptops are 16:9 and some 16:10 so the vertical numbers get even more mushy. Anyway, my point was that even though "4K" as a concept has good mindshare, that's overkill even for a True Retina(tm) experience in the typical OSes on a 13". Around 100 DPI is what those UIs were foundationally designed for (starting in the 1990s) and all numbers unfold from that decision.