Maybe I missed some recent news, but what PDF viewer is pre-installed on Windows?
I'm talking about Reader btw, which would be analogous to macOS's Preview. Edge is like Firefox with PDF.js.
Reader works better than PDF.js too.
So you could definitely print PDFs in Windows 8 from the Devices Charm. You'd just need to know that was what the Devices Charm was for.
(I thought the Charms were a good idea that Microsoft didn't quite know how to execute.)
Having a single place for printing rather than one per application sounds like a nice idea indeed. If only they had documented it better... ;-)
I can understand customer demand but I'd prefer if it was optional - e.g. the first time a user visits a PDF they're prompted to install a viewer if they so wish.