I mostly agree with you in that there are perfectly valid reasons for learning similar languages. The quote is too strong, too absolute. But I still have a weakness for the quote because learning languages that alter your thinking is so much more useful than learning ones that don't.

As to ruby/python, I only have a superficial knowledge of Python, so please correct me if I'm wrong, but my understanding is that ruby blocks let you do thinks you can't in python. Rspec is one of the examples that gets talked about a lot. But if I were asked to sum all the numbers divisible by both 3 and 5 between 1 and 100 in Ruby, I'd do it like this

  (1..100).select{|a| a % 3 == 0}.select{|a| a % 5 == 0}.inject(&:+)

In my mind, that is a completely different way of solving the problem than by running a loop. My understanding is that you can't really do something like that conveniently in Python. Though, like I said, I really don't know python, so please do correct me if I have that wrong.