It seems to be part of the "Plays for sure" spec or whatever they changed the branding to...
Streaming is to a Soundbridge (well, actually a couple of different Soundbridge models)
I'm not really sure how it works, because normally you can only use a smallish number of PCs and portable devices with Napster's DRM licence model, but with UPnP, there appear to be no such restrictions. I guess that sort of makes sense since the devices have to be able to see your network to access the content. I could probably allow people to VPN into my home network and access the content, I guess, but that sounds way too much like doing my day job :-)