Google's single sign on is now live for everything?

Has anyone else noticed this?

http://accounts.google.com

Feels like a tiny bit of the Google master plan has come into view (though I guess this much is obvious to anyone):

1. Build awesome free services

...

x. Build the largest walled garden the world has ever seen

???

x+2. profit

[EDIT] It looks like this has been around a long time and I was just last to notice when I logged into my gmail account the other day.