All metrics are imperfect: this one of course over-represents languages used by employers. It won't capture self-employment (a significant and growing trend). Also, it's uncomfortably common to advertise for one thing in order to filter applicants, when the job is actually for something else. (Maybe it's clever of them, but I've felt cheated by this bait-and-switch.) Along these lines, ability to pick up lesser skills is assumed. (Perhaps that's why PHP doesn't appear.)

Stackoverflow/web searches over-represent languages used with the web (esp Javascript). But, since the web is the fastest-growing industry, it may be an accurate anticipation.

Wow is this common? I wouldn't be surprised. More and more, I see job posts that list multiple languages (more than two or three), and I wonder why they would have such a fragmented setup. But I guess having one script somewhere in Haskell, for example, might help attract a bunch of smart folks but who are then asked to write C# all day. There is a large informational gap between employees and employers unfortunately.

Happened to me twice, and Google once boasted about advertising for python to filter for devs at the forefront - not that they'd actually be doing much python. I guess one could check in the interview.

You may want to correct your spelling of Clojure: http://www.indeed.com/q-Closure-jobs.html