Ruby core api changes incompatibly about 3 times a week. Just kidding, maybe once a week.
Sarcasm aside, shit needs to work. Newer code uses newer ruby apis without knowing it. I support old rubies, so I need newer api features working in older rubies.
Folks on CentOS 5 get Ruby 1.8.5 or 1.8.6, and that lacks things like String#start_with? and Regexp#union... etc. I SUPPORT YOU, FRIEND.
# Example that fails in ruby 1.8.7 and below: % ruby -e 'p RUBY_VERSION, [1,2,3].rotate' -e:1: undefined method `rotate' for [1, 2, 3]:Array (NoMethodError) # And works now. % ruby -rbackport-bij -e 'p RUBY_VERSION, [1,2,3].rotate' "1.8.7" [2, 3, 1]