why aren't my models getting loaded in my app?

gistfile1.rb

# in plugin_dir/lib/plugin_name.rb

...
%w{ models controllers }.each do |dir|
  path = File.join(File.dirname(__FILE__), 'app', dir)
  $LOAD_PATH << path
  # it would be nice if someone updated the documentation.                                                                                                                                  
  ActiveSupport::Dependencies.autoload_paths << path
  ActiveSupport::Dependencies.autoload_once_paths.delete(path)
end

# model (in plugin_dir/app/models/my_model.rb)

class MyModel < ActiveRecord::Base
  # ...

  def my_method
    # does stuff
  end
end

# if I have initializer (my_app/config/initializers/my_model.rb), it loads, and in the console I can see it

> MyModel
=> MyModel(id: integer ... )

# But if not:

> MyModel
NameError: uninitialized constant MyModel

# What am I doing wrong?  Why aren't my models from my plugin loading without the initializer?