Just to play devils advocate - email isn't a great example. In the end, it's become a very centralized service. The protocols allow for decentralization, but these days a very large chunk of email ends up just being data movements in Google's databases and storage systems.

I could go on (the internet itself is moving largely to centralized servers in one of a handful of providers) but the point is - centralization seems to always win out. Can you name a handful of services which started out decentralized and by and large stayed that way? Here are ones which didnt:

Banking, stock trading, email, the internet (defined as computers connected together over tcp/ip), podcasting, blogging, music, gambling, video...

Centralization tends to enable scale, dispute resolution, trust, ability to change. There are downsides to it, but it seems they are easily outweighed according to customers and history.