I don't see the HN example. It has my email address. The only sites/apps/services that would apply here are those that could get by with zero ability to communicate with you outside the site. For instance, if they don't have either your phone or your email, how would you reset your password? How would your identity be verified, assuming other parts of your identity mattered. There may be a use case for what you're saying, but it seems like an extreme corner case.