Why do I need to validate my email when I ask for email notifications, when I am signed with Google sign-on/Facebook etc?
I put it as a bug, as I think un-needed user operations are bugs (But I guess others will think otherwise).
This is needed in the general case. It's trivial for anyone to set up an OpenID provider that claims any email address at all. If it weren't done you could sign email@example.com up for iphone updates with no validation - clearly an undesirable feature.
Email subscription is a one off operation - the validation doesn't hurt it much and special casing specific providers isn't great either.