That's really a comment about your distro, not about Ruby or Rails. It /should/ be as simple as installing Ruby, then `gem install rails`. If it's not then something is broken with your distro's package.
"gem install mysql" or whatever and it just works.
But the issue comes in when it doesn't work, which it didn't for me. It took hours of debugging. MAMP gets me up and running in < 5 minutes. A proper LAMP setup takes me < 10 minutes. I'm failing to see the advantage of Rails (at least from a setup standpoint) when it works perfectly most of the time, but fails so hard.