And that's just the tip of the iceberg of languages that seem to somehow have missed the adoption that they definitely deserved. And, conversely there are plenty of languages that did not 'deserve' the recognition they got.
It's almost like fashion, some stuff makes perfect sense but will never make it, other stuff is pointless and a smash hit.
"Undervalued" is quite different from "misunderstood". Most of the languages you both listed are not quite known even emong programmers; on the other hand, anyone who's evenr dabbled with Web production (and many that just browse) have at least heard of Javascript. Douglas' point is that many people think that they know what Javascript is all about, but they're wrong.
(Note: This opinion is probably naive or uneducated)