Yes, "everyone" doesnt mean "anyone" it means everyone from that domain/homegroup etc. Note that share credentials is specifically mentioned in the Wiki setup instructions
I guess I can see why you think it's peculiar, but to me that just means we havent been clear enough in an overall explanation of how this addon works and why we (well, krusty mostly) built it. It is for those former WMC users who want to use TV in XBMC, but increasingly also seems to be newcomers who have a windows box even if they didnt previously use WMC. We cant/dont access the stream from the tuner, we only access the WMC EPG and Recording services. We get WMC to record the stream then send that to XBMC as a TS file (because there are problems with playing a growing WTV file). Possibly we could read the file and send the stream data to XBMC rather than a file but that is a whole lot more advanced multiplexing code etc and we arent video programmers
The whole approach of this PVR addon is to tap in to microsofts WMC services which gives us broad support of a whole range of tuner hardware, broadcast standards/countries/providers, EPG's whether its download or OTA scraped, and the rich features of the WMC recording service such as tuner conflict resolution custom pre/post padding etc. It isnt our intention to directly talk to tuner cards or add special support/features for just 1 hardware device out of the 100s/1000s that are on the market.
Like you say though, "it just works" for many of us so that is reward enough, that so many people from different countries and types of setups are able to use XBMC to watch TV, and although your case has had some setup difficulties (due in part to not following the instructions regarding ensuring the directory is shared and accessible from the client!) it's one of the easier addons to setup and have working