>Computer UIs need animations for the same reason they need shadows, gradients, and momentum: because these are aspects of the physical world that we already know how to interpert, so can be used "for free" to aid our understanding of the UI

More like "for the same reason a fish needs a bicycle".

>Not using animations would likely be more taxing on our visual processing

And yet, Windows 2000 era UI was far more intuitive, consistent, and self-discoverable than today's animated, shadowed, gradient-filled, blurry transulcent, momentum-having flat crap.