This is a great demonstration of why to use CSS3 animations - Flash doesn't support the concept of graceful degradation. This page turns into a static image in Firefox/Mac instead of borking out with a blue lego piece.
As a developer, here is why i(personally) wont choose CSS3 animations for building similar content anytime in the near future:
-Works only on webkit browsers
-Performance is really bad on Chrome. Compared to most of the heavy weight flash content out there, this is just a very basic animation.
Really? How? I was an actionscripter for years before I dropped Flash from my arsenal and worked at a game company that would've loved to provide their games on systems without Flash.