Woah there. I don't agree with this. The web is certainly not centralized (this is on Hacker News and not Facebook, right?) It follows a power law distribution where you have some players getting lots of traffic and then there are lots and lots of small traffic sites. But it's definitely decentralized.
_Google_ is something of a monopoly providing some of the features you list for the web at large, but there are others (Duck Duck Go, Bing) that are just a click away.
Gmail took a huge share of the email market by being a better product for the first several years of its existence (and being free also helped). That doesn't mean email is centralized: I've been using Fastmail for the last several years and it works _just fine_. I don't have the problems you list.
Anyhow, I agree with your point that a decentralized _social network_ needs to solve the problems you're listing. I just think the web and email are actually examples of technologies that remain decentralized.