Why Does This Work?

So I am going through Peter Armstrong's Flexible Rails book.

In Chapter 5, he talks about fixing ActiveRecord's to_xml() method. I am a fan of Rails, but I am not a fan of the solution he chose in his book. IMHO, it's kind of ugly and un-DRY. In other words, inelegant.

My first attempt at a better solution is to write my own to_xml() method, which is as follows:

def to_xml(options=nil, &block)
  super options == nil ? { :dasherize => false } : options.merge(:dasherize => false), &block
end

I pasted the above into each of the four models defined in the Pomodo project Peter guides his readers through in the book, and it works, albeit un-DRY.

Then I did some reading on how I might override the built-in method at a single place, and came across this article. So I then removed the code from the model classes and placed the following at the very end of the pomodo/config/environment.rb file:

class ActiveRecord::Base
  def to_xml(options=nil, &block)
    super options == nil ? { :dasherize => false } : options.merge(:dasherize => false), &block
  end
end

To my surprise, it works, too. It has fewer lines of code than both my first stab and Peter's solution, and it is very DRY. In other words, it is elegant.

But now I am left with this question: Why does this work?

I am not as well-versed in Ruby/Rails. Can someone help enlighten me?