Even email is centralised these days. Look how many providers host over 90% of people's primary email address.
If the case of a social network, you can't just switch and still remain connected with everyone else, because the provider controls the flow of your interactions. However, you can very easily switch your email provider, or even host your own, and as long as your friends still have the same emails, you're still "connected". I wouldn't call email centralized, but I agree is not decentralized 100 percent.
More generally, I think there's an incentive problem here: it is just too convenient to let Big Data host your email. And if you're crazy enough to have a mail server at home, it is just too convenient for everyone else to spam-filter you as a netbot (because you're using a residential IP address).
decentralized technologies would promise to benefit all participants; but i guess the problem here is legal protection; a registrar based on blockchain is a contract that would require legal recognition; how easy would it be to achieve such a change?
http://en.wikipedia.org/wiki/Legality_of_Bitcoin_by_country
this article has lots of words even when the currency is legal.
Still, decentralized systems (in the context of the article) are great, but they present one little challenge: What incentives do people get in order to host a participating node/agent? In the case of bitcoin, the miners get a reward ($) each time they solve a new block, but unless all these decentralized systems leverage an existing blockchain/cryptocurrency system and have a system of rewards of some sort, they'll have a hard time springing into existence.