2.3 to 3.1 upgrade: RESTful routes now required when using link_to("foo", @object)?

I’m upgrading my application from Rails 2.3.11 to 3.1.1. After
updating my routes file with the new syntax, I’m seeing a change in
behavior of the link_to method when passing an ActiveRecord object as
the link destination.

Here is an example of an old (non-RESTful) route from my 2.3
application’s routes.rb:

map.with_options :controller => 'widget' do |widget|
    widget.widget 'widget/show/:id', :action => 'show'

Here is what this route became in my 3.1 file:

controller :widget do
  scope "widget" do
    match "show/:id", :action => "show", :as => :widget

The output of rake routes is similar. 2.3:

widget /widget/show(/:id)
{:controller=>“widget”, :action=>“show”}


widget /widget/show/:id(.:format)
{:action=>“show”, :controller=>“widget”}

What’s different is that now my link_to calls that look like this:

link_to(“Text”, @widget_object)

Produce this error message:

“Routing Error: No route matches
{ :controller=>“widget”, :action=>“show”, :id=>#<Widget id:
123, …> }”

After seeing this passage in the Rails Guides:

“<%= link_to “Magazine details”, @magazine %>…This allows you to
treat instances of your models as URLs, and is a key advantage to
using the resourceful style.”
Rails Routing from the Outside In — Ruby on Rails Guides

my guess is that Rails 2.3 happily handled my link_tos because my
named route was widget_path/widget_url (changing the name would cause
my 2.3 app’s link_tos to break as well), but Rails 3 insists on
RESTful/resourceful routes if you’re going to use this link_to style.

Is that right? I’ve started refactoring and adding the necessary
RESTful routes to make my link_tos work again with good results
but I want to confirm that I really understand the problem.