I'm shocked.
There are good reasons for this, but how much of it is political garbage?
This is similar to what Apple did with iOS - they couldn't outright ban the internet, but they made it impossible to circumvent the app store. You can't write a HTML game that uses graphics as advanced as a native app, and you can't write a web app that accesses arbitrary (non-cooperating) network resources. You have to go through the app store, Apple get's their 30% share. You can't write guerrilla apps that aggregate data from non-cooperating sites, or that do e.g. P2P file sharing - if what you're doing is illegal (or not wanted by Apple) in US jurisdiction, they have you're address, and you're in trouble. You can't even write a runtime or a tweaked browser to circumvent all this, as they explicitly forbid it.
The reasons why Google is pushing a similar strategy are a bit hazy. But it's clear that rich clients are a threat to Google's business model. Google profits most if everything happens in the web.
This is part of a larger war on general-purpose computing. Just look at the Metro apps in Windows 8/RT, the fact that OS X by default now only runs signed applications, or ChromeOS.
I only hope that we can keep DRM out of the open web as long as possible and have it die when plugins die.
Seems more like a case of "not invented here" syndrome rather than "Let's Be Evil"
Plus, most plugins are proprietary shit, holding back standardization and everyone knows it.