"One reason is that the average skill level of programmers who know Ruby is higher than those who know Java, for example."
Had to double check the year on this one. Things must certainly have changed... For instance, Java is a staple of most CS curriculum. If not Java then often Python. /Never/ have I heard of Ruby being the primary language of choice by a CS department. (Nothing against Ruby, just an observation.)
On the other hand, what is the most popular language/framework for a beginning programmer to learn today? Ruby/Rails or Node? Whereas Java is the quintessential Corporate language.
I'm obviously making some generalizations here. But things certainly seemed to have changed a lot!