Yaron Minsky said in one of his talks that hiring OCaml programmers was the easiest thing in the world: he posted an ad on the mailing list, got 20 applications, 15 of which were worthy of a phone interview. Of those 15, 5 were asked to come in for an in-person interview and 3 of those were hired.
Sure, he might not be able to hire 80 programmers in one batch, but I don't think Jane Street would need to do that, or that they are worried about a shortage of OCaml programmers. Also, I would be more confident of the capabilities of an OCaml programmer than of a PHP programmer.
What it means is, People who learn OCaml generally have to learn something else too. Because the jobs just aren't there. Which in case the person is better off learning that something else properly.
I generally pass over resumes where someone doesn't list at least one programming language that isn't very marketable, fashionable, or part of C's extended family. It's a quick way to winnow out folks for whom programming is likely to be more than just a paycheck.
Sure, he might not be able to hire 80 programmers in one batch, but I don't think Jane Street would need to do that, or that they are worried about a shortage of OCaml programmers. Also, I would be more confident of the capabilities of an OCaml programmer than of a PHP programmer.