Does this also apply to end-users of Ruby apps that are just an apt-get away? I don't really want to learn all that stuff (and remember to redo it on all installs) just to use some tool that happens to be written in Ruby.
Re. bundler/gems, I don't know what those are - the file "core_ext/hash/conversions.rb" I hand-patched was from a package called ruby-activesupport-2.3 which is a dependency of the Rails package.
I think if 100% of your eco system is from the package manager you would be fine, but if even a single component needs to come from outside I would reach straight for rvm and bundler (no prejudice against rbenv, rvm is just what I use)