Did you find the solution? I have currently the same issue and I don't figure out how to block this task.
All the settings in my publish service does not impact photo rendition. So I don't need to re publish all.
The users get confuse with that.
I have the same question as well, never figured it out.
I believe the example provided is flawed and here's my proof: If you edit description of a Flickr publish collection, you get "republish all" dialog. If you do the same on Facebook publish collection, the plugin silently accepts the changes. So clearly, the Facebook publisher plugin is doing something that the Flickr plugin is not.
You could try contacting Jeffrey Friedl -- he's probably the most knowledgeable person outside or inside Adobe about publishing plugins. I believe he designed the publishing-plugin architecture under contract to Adobe. I've never seen him participate in these forums but he's pretty responsive to his customers, and he might respond to a direct query.
Jeffrey is the man! The solution is simply:
function publishServiceProvider.didUpdatePublishService(publishSettings, info) return true end
The return value is not documented in SDK. I wonder if there's similar hidden meanings with other callback methods?