Development tools often are, but almost never exclusively using ruby gems and it's certainly not a universal practice. ANd of course non-dev tools can't be distributed this way.

I think of Rake/Rails as dev tools that are executables. In the post, I mentioned passenger because that was using Rubygems as a distribution mechanism and then they stopped doing that. I don't know if it's a hard / fast rule or even who would enforce that rule ... I was just mentioning that maybe it's an anti-pattern?