And it suffers from the same limitations as any other attempts at filesystem sandboxing – it only caters for the simple "open/save one file" respectively "open/save within one folder (plus subfolders)" use cases and ignores (and breaks) the existence of any other workflows.
Win32 applications on the store run with trusted identity, so it allows for a bit more than that.
“This App is provided and updated by X.” I don’t know what more you expect them to do.