True, but for those who do experience a ban by any major SSO provider they're straight outta luck. With FB/Twitter/Amazon SSO you can at least contact the sites you're locked out from and provide your email address to prove it's your account and hope the administrators actually have a workflow to convert a SSO-bound account to a "normal" one - but not when the only "proof" method is your mail address which is gone.
I always tend to think about the 1% edge cases, because these (and the resulting bad press!) can be those with the biggest amount of time required in customer service, and in addition they're hard to set up in a way that isn't vulnerable to phishing.
