> It is true that all message responses (including accessors) are implemented using methods.

An object can respond to a message even though it doesn't have a method with that name. A classic example are Rails' dynamic finders:

  User.methods.include?(:find_by_name)
   => false
  User.respond_to?(:find_by_name)
   => true

> An object can respond to a message even though it doesn't have a method with that name.

Sure, by using a different method (method_missing); its still all method calls.

Yes and the responses are implemented with methods. Always.