I'm pretty sure that there's nothing prohibiting you from bundling the Ruby (or other) interpreter with your app, as long as the code that it executes is static (i.e. doesn't allow the user to execute arbitrary code). It would probably cost a lot with respect to the size and possibly speed of your application, but I thought that I'd note that it is at least possible to use some other languages.

Kind of a blurry line. If you have a button on your screen, an "arbitrary code path" can be run when the user pushes the button. That is apparently fine. So it follows that running similar codepaths based on strings in a text file is also fine. After all, the user isn't writing code, he's just controlling the program (the $foo interpreter) with his input. Clicking a button, controlling a runloop... both seem exactly the same to me.

I am sure there is some arbitrary line drawn between the two, though, which is why I don't even bother. If Apple thinks they can make money like that, great. I don't have to help them though.