I realize it's politically incorrect to consider a person's accent with the quality of a screencast, but some people will not watch if they cannot easily understand what's being said. I seriously don't feel comfortable saying this, but it has to be said.
I would argue that SOAP introduces coupling through bad implementations, which is much easier to do since SOAP is complex. It sure would make sense if at least .NET's implemenation would resolve and generate SOAP messages as interfaces
You mention your logic on the placement of buttons in the AppBar. I don't proclaim myself as an expert, but I think you are mistaken, or at least it seems wrong to me. I agree with the logic as stated by Microsoft's guidelines, though I think your understanding of what global means is incorrect. I will assert that global means the functionality is shared between more than one page (perhaps all), while local is specific to one. If this is what you're doing, then "select all" should be paired with "clear selection".