I think you're absolutely right to draw that parallel. But, today's email landscape isn't much of a federated open standard. It's a web of trust and distrust, filters, and deliverability issues. It's real work to maintain an email server and attain high deliverability with other email services. So much so that most don't even do it anymore. Most email is just delivered by a few large providers.
Really, email is suffering from a lot of the same issues that PSTN also suffers from. But email providers just decided to "solve" the problem themselves, mostly by taking a heavy hand at blocking things and deciding they don't really care if you're not a big provider.