What if you'd like to develop a gem not for any specific platform? What if you want to develop desktop apps, or make CLI apps to automate little things on your usual platform?
I guess it just depends on the target. For starting out serious development I'd certainly agree with all you say, although I personally prefer the local development and tests on staging method, since it means I know it runs on at least two systems, at least with the code where it's possible. It might be nicer for beginners though to be able to quickly dive in.
