On my Android Phone ( 4.1, Galaxy S2 ) the demos ran very quickly on the stable version of Firefox, but the stable version of Chrome struggled greatly until I enabled webgl in about:flags.
Even with webgl enabled, Chrome was still a bit slower than Firefox on the bunnies demo.
The flashvhtml site and game that was posted here a while ago also uses pixi.js. http://flashvhtml.com/
The html5 version of the game there runs very well on both Firefox and Chrome with webgl enabled on Android.
"No mainstream 2D rendering system (not X.org, not Mac OS Quartz, not Windows GDI/WPF+DWM) uses any graphics acceleration to draw 2D primitives."
That isn't entirely true.
Windows has Direct2D for graphics and DirectWrite for text after all.
Direct2D and DirectWrite were first introduced for Windows Vista and 7 using Direct3D 10. Windows 8 expanded it using new features found in Direct3D 11.
You can see the high performance and fluid animations it brings in many of the Metro applications. Desktop applications need to migrate their existing code of course. IE and Firefox have done this already.