[chef] chef_gem vs. gem_package

[Sam Darwin < >]

from the documentation:

Warning
The chef_gem and gem_package resources are both used to install Ruby gems. For
any machine on which Chef is installed, there are two instances of Ruby. One 
is
the standard, system-wide instance of Ruby and the other is a dedicated
instance that is available only to Chef. Use the chef_gem resource to install
gems into the instance of Ruby that is dedicated to Chef. Use the gem_package
resource to install all other gems (i.e. install gems system-wide).

from observation:

gem_package will fall-back to chef_gem behavior if ruby isn't on the system.  
 
have you seen this?  Am I imagining it?     The problem is that you don't get
consistent results from a recipe.   If one machine has a system ruby 1.8,
another machine has chef-client (with ruby 1.9) and no system ruby, very
different things can happen with the same recipe.     Should the meaning of
chef_gem vs. gem_package , and the differences between them,  be more 
enforced?