That's kind of the point, isn't it? I use the languages that I am most familiar with, because I am far more effective with them than I am with whatever this year's new awesome language is.
If I had been doing Ruby from the beginning, then I should continue doing Ruby, and not use C++ just because someone else says so. Likewise, if I've been doing C++ for as long, it doesn't make sense for me to switch to Ruby just because someone else doesn't like C++.
This stuff is so much nonsense. I think I will start using programming language evangelism as a reliable marker of a less experienced programmer.
Unwillingness or inability to shift between development tools where appropriate is also something I've noticed characterises less experienced programmers (often evangelism can be driven by this).
Using your example languages. I can think of situations where using C++ rather than Ruby would be idiotic, and likewise situations where the reverse is true.
Because, from what I've seen, a lot of people can be very excellent programmers in one language, but be unable to learn to program in another.
Actually, I don't think it's really "less experienced programmers". Several of my computer science peers (I'm 23) -- inexperienced as professionals, but very smart -- will try the same problem in four or five languages, just to learn the language, and have no fears about jumping into a new language to start a new project. On the other hand, I know some excellent older programmers (late 40s) who know C++ super well, are willing to apply jaw-droppingly complex template metaprogramming, but who only reluctantly use Python and won't touch Ruby or Scala. It's probably more of a cultural thing.
I don't think it's cultural, or even generational; it's just the byproduct of working in a domain for a long time.
Inexperience doesn't mean a person isn't smart, or that they aren't good or that they aren't clever. All it means is that they haven't developed a significant body of familiarity with something.
So, your peers are learning several languages -- maybe superficially, maybe not -- but they aren't yet developing the familiarity with one or a couple of languages that allows them to feel comfortable mentally solving any given problem in the language they're most familiar with. Thus, you have "Ruby" problems, "Python" problems, "C++" problems, and so on.
Those older'n-dirt programmers on the other hand have already solved a huge number of problems in C++. That doesn't mean they're a better programmer, but it does mean they're more experienced. So, if you ask them if they could write X or Y or Z, they'll say sure -- and in their head, they're probably already gathering the familiar pieces that they would need to solve it.
Or, to put it another way: if you went to pg and asked him to write software to run a forum like this, he would probably choose to do it in Lisp, and that would be a good choice for him. If you asked me, I would do it in PHP. If you asked DHH, he would do it in Ruby (on Rails).
None of those are wrong.
The only wrong choices would be me coding in Lisp.
You can justify using any language by saying that. Such a vague statement.