It's akin to confusing a linguist with a polyglot, a top-level accountant with a research mathematician, or someone who writes HTML with someone who programs in Python. They are simply different. Not getting it right is either a mistake, or a demonstration of lack of knowledge of the difference.
EDIT: Added the first parenthetical clause.
I'd like to say 'Thank You' to the HN community for brutally enforcing both clarity and accuracy. You guys are the best proofreaders ever.
And people that teachs despises people that "work" and vice versa.
Most of my friends despises people that teachs ("they suck on research funding for useless purposes") while most of my wife's friends despise people that sell they work on the corporate space ("they do not create any new knowledge").
I personaly think that both are right as they understand the political game at hand and play it.
(One exception is the IEEE, which puts author bios with their academic pedigree and current position at the end of every paper, and attaches "IEEE Fellow" in the author list to those authors who are IEEE Fellows.)
I mean, seriously. When was the last time you saw something say "Dr. Knuth"?
You won't see that very often -- Knuth is particular about including first names (or rather, their initials). He got quite upset with me when I wanted to be "Colin Percival" rather than "Colin A. Percival"...
That said, you will see "Dr. D.E.Knuth" in any sort of formal situation (e.g., a visiting lecture); even if "Knuth" by itself is enough, it's simple politeness to provide a full title.