A consumer might have to do specific badge checks for restricted sites like the WoW forum example (I agree that I would never use this feature myself, but I can see some value in it), but they would clearly know exactly what they were looking for beforehand.
Publishers: WoW forum, StackOverflow, HotOrNot.com
Consumer (me): Hacker News
As HN, I obviously don't want to display the HotOrNot badges, probably just the SO stuff. So, I set it up to pull those. Not too bad. Now imagine that there are hundreds of producers, some that make sense, and many that dont. You probably have to do a fair amount of digging to find those that make sense for your site, and a lot probably fall into a grey area. Then, you may find that only 1% of your userbase uses any particular 3rd party badge-producer. So you have a choice: include lots of badges, most of which will mean absolutely nothing to 99% of users who see them, or include only the most popular badges, which means the service ends up dominated by a few big producers (Twitter, Facebook, etc.).
I guess I'm having difficulty articulating, but I'm just thinking that as someone who runs a community site, I don't want to go digging through dozens of other sites' badges to determine what they mean and if they're applicable to my site. Plus, I don't want to have to re-do this every couple weeks to add any new badges that have appeared in the system. And, the only end result I see is being able to decorate user profiles with bling that is meaningless to the majority of the other users on the site.