When I returned to Rails after a couple of years away from it, I had to piece together a few different blog posts about setting up Rails 3 with Ruby 1.9 on Mac OS X to get my toolchain working, and even then I had to troubleshoot version-specific problems not covered in the blogs. I believe most beginners would have been deterred from continuing. I don't really use Rails on Windows much at all, but tried RailsInstaller on Windows 7 just for fun about a year ago and was delighted it worked so well and would like for beginners to have such an easy experience on a Mac, my OS of choice!