In my experience, autistic-ish people (often geeks or nerds) sometimes confuse being polite with being social, which does take time. They then seem to think that if they don't have time (or really, the skill and desire) to be social, then they don't have to be polite.
This is a minority of geeks and nerds, of course.
That's exactly it, though. Politeness and terseness are often diametrically opposed in our society, and since there is no standard of politeness outside what society finds to be "polite", I'm not sure how you can say many people have an inability to distinguish.
If you email a long question to someone and they respond with "No.", many people would find this to be impolite or downright rude. It might be the most efficient thing and the hacker-type might think it's OK, but if most people think it's impolite, it is.
This isn't the end of the world. I'm kind of a jerk.
How do I respond politely to a four page essay without spending a significant amount of time on it?
But if he as a human has to have some personal flaws, am fine with sacrificing that.
Furthermore, politesse is not a lingual phenomenon. The politesse of a Texan is different from a New Yorker is different from a Minnesotan is very different from a Londoner.