Just me being nosy.. why are some classes autoloaded and some classes required? 

Basically autoload loads constants when they are first called, and require loads all of them at once. Autoload is boosts performance, but there are some [issues](http://stackoverflow.com/questions/8617368/lazy-evaluation-with-autoload-vs-require-in-ruby) with it not being threadsafe, and there we're speculations that it was supposed to be deprecated with Ruby 2.0, then with Ruby 2.1, but no one knows its future. 

I guess it is safe for now to be used, but to return to my original question - is there a reason why some classes are autoloaded while others are required?