Maybe in some vague way - but in a technical sense, not allowing the user to implement or install their own protocol handler very much goes against the historic

Maybe in some vague way - but in a technical sense, not allowing the user to implement or install their own protocol handler very much goes against the historical spirit of Windows. But then again, so does ads in the shell. But Windows has always allowed vast, fine grained programmatic read/write access to anything the running user has authorization for, and for admins that's almost everything. Certainly everything in userspace, such as URL protocols.