Just for a moment, consider who this man is and what he has done. We would all do well to take a step back and consider his manner of response. Notice that he continued learning new languages after creating Erlang (instead of just evangelizing it at the one true language). He did not immediately say "choose these three languages" as if they were the only ones you could possibly learn.
Does it really help our profession/hobby at all if we engage in language-elitism and snark? Even on Hacker News I've seen vitriol directed at Ruby, Python, Javascript, Haskell, to name a few recent targets. All languages have their place, even if that place is only as a lesson for future language designers.
Encouraging people to build stuff, whatever the language, whatever the library, whatever the framework; that is what we should be doing. IF someone wants suggestions, or help deciding what to use, that is fine, but criticizing someone for the language or framework they use has become all too common and a stain on the character of our community.
That's not to say honest criticism is unwelcome: All languages/libraries/frameworks/software can improve. But to belittle people for the choices they make, or to segregate ourselves into voluntary language-ghettos we are compelled to stay in by the force of public opinion...that goes against the spirit of what people like Armstrong worked hard to build. Maybe it started with "Worse is Better", maybe it started with alt.religion.emacs being taken a little too seriously, but it has been perpetuated by all of us, even Paul Graham (in Beating the Averages).
At some point, this has to stop. We, as a community, must grow to support the betterment of hacking by creating and encouraging creation; not by petty vitriol and conformism based on fashion.
Now, I've strayed pretty far from the point of the post itself, but Armstrong closed with such a salient point: If we stopped bickering so much about what is the "right language", "right framework", "right library" and instead encouraged particular protocols and documentation standards we'd all be better off for it.