I think age plays also a role. I have met various young people who have't entered the "working world" yet, that only have an email address because they needed one for registration and to recieve some school related information. But it is percieved as something completely arcaic and they never use it for anything else nor check it regularly. All communication is via messangers or social media.

On the other hand also elderly are or could be moving in this directions. E.g. my mother getting an iPad and apps like Whatsapp have completly changed "computers" for her. From, being mostly a chore that you have to use, to something really useful for getting information and to stay in touch with relatives in other countries

He does mention, somewhat off-handedly, that the lack of email makes password recovery harder. (Presumably impossible without some other communications channel like a phone number.)

And you really need to be able to recover account access for a paid subscription. It's probably also reasonable to assume that if someone is going to give you a credit card number and address, they're probably OK with giving you an email.

I run a site that takes payments for a subscription, but then just stores a cookie on the users machine proving they've paid.

It will give them the cookie again if they re-visit from any IP they've previously used.

It also re-gives them the cookie if they try to pay again with the same credit card.

Support just tells people to try to resubscribe if their subscription has 'vanished' - but it seems to happen to very few customers.

This is pretty clever, but people might get double billed if they accidentally try to confirm their account with a different card than they used to sign up.

Public IP as an auth token seems like a horrible idea.

You're giving anyone on CGNat or even the same coffee shop access to your customers account.

In my case, customers don't have any data on the account - it's simply a bit saying 'has paid for premium?'. And if I end up giving premium to a few people who didn't pay it isn't an issue. The sign-up friction of needing an email address is greater.

How about you put the recovery code onto the invoice / credit card line?

I would suspect brand too makes a difference in whether people will give away their email address.