wouldnt this be the case for any vendor you choose?

yes

Indeed. But some are easier to change than others. I switched my e-mail provider, and it took all of five minutes to launch the copy of my data. Since I kept the same domain, everyone sending me e-mails didn't notice anything.

With Apple's approach, I'd have to go through each account and move it from something@icloud to something@new-domain.

However, for people who don't want to mess around with custom domain names and e-mail providers, apple's approach is very practical. You just need to tell it to "hide your email" when you register somewhere and you're good to go.

In my experience the overwhelming majority of services permit me to change my email address.

Of course. But I have hundreds of user accounts, as probably many people do. I would not enjoy changing all those email addresses.