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.
