So, in other words, it doesn't fit into preexisting languages idiomatically. You want to introduce new idioms into Closure to make it integrate better with the JVM.

That's fine, but it also means that if you want to do a direct port of, say, Ruby or Python or Erlang, you'll have several rather large warts compared to new languages designed to run on the JVM and use the Java class libraries.

iteration and getting system setting stuff are so generic you might as well implement it yourself or write a thin wrapper (in this case iterating over entries in a hash table and getting the OS name)

IMO, a good chunk of the java libraries are there to overcome java deficiencies, and don't produce anything grand on their own for other languages.