> Hence Twitter runs on Scala, Blekko runs on perl.
Those are hardly equivalent (aside from the obvious differences in prominence, scale and relative importance between Blekko and Twitter).
Scala shops attracts developers curious about new paradigms (FP / FP hybrid) whereas Perl shops tends to repel forward-looking developers who view it (accurately or not) as an ugly throwback to the year 2000.
Put plainly : Scala sells itself (to a certain crowd) whereas Perl needs to be be sold almost across the board. Scala is viewed as an up-and-comer, Perl as a has-been.
The parent was making reference to the common notion that using outlier languages provides access to high quality talent. In certain cases this holds true, in others not. You will attract, on average, higher quality talent by using Clojure rather than Cobol.
EDIT (response to parent edit) : well, no. I never said there are "no good Perl jobs", just that Perl is not in and of itself a draw in the way that Scala / Clojure / Haskell might be. You could probably convince someone that there are cool opportunities in Fortran development, but very few are actively seeking them out.