I'm a big fan of Rails, but I think that Rails does not really give a lot of weight to backwards compatibility. The Ruby community in general often feels like it's always charging forward, very often with tons of cool new things, but occasionally leaving broken, incompatible software in its wake.
You seem to imply there is something wrong with that.. As long as you bump the version number and support the old version for bug fixes, it ends up being the best way to move the world forward.
I am a fan of Rails and am doing some work on it, but it's pretty clear that while Rails is bumping version numbers cleanly, they aren't putting all that much work into supporting older versions. Github has been doing their own work backporting security patches to Rails 2.3 for years.
