I don't use Ruby at all, personally. I use Python and Bash almost exclusively. I use Puppet but am not a huge fan, and I certainly have no plans to switch to ruby. I mostly agree with your original point.
However, the CLI thing is a legitimate advantage in favor of Ruby and Perl. Python is just really annoying to use for system administration one-liners. A number of fundamental design choices that have a minimal impact on even the smallest .py files make 'python -c' cumbersome.
Specifically:
A number of common tasks available as syntax in Perl and Ruby are in libraries in python. In particular, you often need to import sys, os, re, and subprocess. Not a real issue writing scripts, but adds a lot of overhead to a single line.
You can't pass a DEDENT token to '-c', at least I haven't figured it out, meaning you can't use more than one loop or control structure. You can work around this to some extent using list comprehensions.
Python's string literal syntax is more limited. I have never had an issue with this writing scripts, however from the command line it can be annoyingly tricky to keep track of which quote characters are needed. Ruby and Perl both have non-conflicting options for notating string literals. In shell scripts, strings are the default literal and you only need to worry about keywords and special characters.
Another advantage of shell are list literals. (I don't have enough practice to know how Ruby and Perl fare in this regard).
Bash also has some extremely convenient list expansion syntax.
for fqdn in {www,news}.ycombinator.com ; do echo $fqdn ; done
python -c "import sys; [sys.stdout.write('%s\n' % fqdn) for fqdn in ['%s.ycombinator.com' % sd for sd in ['www', 'news']]]"
Obviously this particular example could technically be shorter, since I could use for-loop syntax (and in python 3+ print is a function). But I would have to arrange it like this if I needed another nested loop. If you wanted to perform some additional action on the names you might have to import yet another library.
Incidentally, C can be a useful admin tool if you know how to use it, but usually the compile-execute cycle makes it more cumbersome than it's worth for one-offs. A C compiler might not even be available on your production system.