The sad march towards tribal fiefdoms continued Thursday, as Google announced that it will only allow Chrome for Windows users to download extensions hosted by Google's own Chrome Web Store starting in January.Google says the decision to transform Chrome into a gated community stems from security concerns, in an echo of the official reason that Microsoft moved to the Windows Store model to distribute modern UI apps. Google engineering director Erik Kay points the finger at the damage caused by rogue extensions in a blog post detailing the lock-down.