[pmlnr]

It's true that when or if you need to communicate with them, you need to play by their rules, but it's also true that email has the potential, the power, and the technical solutions to shift away from it, should it ever be needed or wanted. This is not true for centralised by design systems.

EDIT: I don't think people will be able to abandon email, given it's a replacement for paper mail (banking, official papers, etc). If the big players won't play nice, people will need to get to another provider, simply because the source of email won't be willing/fast enough to jump on [system X].