That's true but you could say that about zsh too, and any number of other languages. Usually, the important reason that shell programming is used is the lack of need to install anything to run a script, which makes it easy and portable, and hence, reliable.
I can't write a script in Ruby and share it safe in the knowledge it will work on another system, especially if it relies on a gem or two. I'd much rather go with something that compiles and move a binary around if I'm dropping dash/bash/zsh. If I was forced to choose an interpreter to do that kind of work, perl would be much safer than Ruby, Python or Javascript.
completely agreed. on a linux system, most of my shell scripts are written in ruby at this point, simply because it is much better to work with than bash.
I'd say it is custom webapp development (with rails) and scripting on the command line (anything bash can do, ruby can do better).
PHP is good on the web with the huge installed base of wordpress, but when it comes to custom web app development, ruby (well, rails, really) holds its own with laravel, symfony and the other MVC frameworks.