It was missing some keywords from the Ruby 1.8.x trunk, and the few additional ones from the Ruby 1.9.x trunk.
Also, it did not contain certain Interpreter defined aliases and constants, that are mandatory (no option on our part, they are always defined.)
As such, these constants and aliases, are in effect, keyword extensions. (Several of them are aliases for keywrods, ie TRUE = true, etc.)
For those who argue that constants are not keywords, I submit that these particular constants, must be treated as keywords, and highlighted in a way that informs coders that they are special, and not to be overridden or redefined (unless you are a very experienced rubyist, and absolutely know what the "bleep" you are doing.) Changing these constants, can break all other Ruby scripts running. So this is why they are now on the list.