They've been wanting to do that for years. But getting the protocol right was the problem. It is an add-on now, but will be part of the browser soon enough I'm sure.
They tried to utilize OpenID first, but that didn't fit the use case. They had to search for OpenID-buttons in HTML to make it compatible with existing sites and that wasn't reliable I guess.
It actually worked quiet well, a working demo-page seems to be MIA right now.
They are obviously trying to solve 2 things with all these developments: Trying to create useful things and trying to stretch the existing technology. And come up with standards and specifications which all browser vendors can implement.