I don't think this is the story's main point. If Facebook rolls out an AdSense-like product for publishers they're effectively building an external ad network (external as in outside facebook.com, not outside Facebook), right?
It does not matter if site already has any Fb services (likes, recommends, sharing)- Facebook callback could be easily added to any site together with advertisment module. It means that Facebook will deliver to ad module that ad that is most likely will be clicked according to site's user fb profile, likes, etc.