There appears, to me, to be some correlation between intelligence and blunt communication (nerds speak bluntly, mundanes politely) but that could be intelligence and contrarianism, or any other of many potential factors

My pet theory about this is that intelligence correlates with not fitting in socially, which then correlates with deliberately doing things differently to prove that not-fitting-in is a choice. If you hang out in any subcultures (goth, roleplaying, etc), you'll tend to see a lot of that kind of countersignalling. I guess that's a point in favour of your contrarianism argument.

Another alternative is that intelligence correlates with realising that communication styles are just styles and not the natural order, which then frees them up to switch between styles at will.