Yes, and it's nothing new, you can do the same using Debian and then select the most appropriate version of ruby with update-alternatives... RVM and rbenv do something different, they allow you to _run_ different version of ruby for different apps. The fact that you can use them to set the default ruby for your system* is a quite handy side effect.

* And even then, you don't set the default ruby for the entire system, you set it for your own sessions.