I can't access the article but looking at the homepage, I'm surprised it's not just a giant spritesheet that changes the x/y offset on certain intervals.<p>Nevermind, it is a giant spritesheet, but it's optimised to allow for static elements to not have to be redrawn.
<a href="http://www.google.com/logos/2011/graham11-hp-sprite.png" rel="nofollow">http://www.google.com/logos/2011/graham11-hp-sprite.png</a>