Do you mean features the Ruby *language* gives you out of the box, or
features that Ruby *libraries* give you out of the box?
In a lot of the cases it is the language. The richer functionality for strings can be overcome by reimplementing the missing features (split a string on a regexp, handle unicode codepoints) but then the question arises "Why are you using Lua when you are just reimplementing Ruby". I tend use Lua when Lua the language provides the features that I require. I know that with some effort everything that can be done in Ruby can be done in Lua but why bother?
Time spent making language X work like language Y is not productive, just use language Y and be done with it.
