Until you change ISPs and your ISP provided email address goes away. Sure you could say use gmail or yahoo mail, and that is obviously just fine until they become "evil" or go out of business. Or heck you get your own domain and want to migrate over to using it for email. I have had a number of email addresses over the years and most of the old ones I have lost access to, how does that work again?

Exactly as well as OpenID, only it's a much better understood problem and avoids a ton of confusion?

You just change your email on record. This is not a hard problem.