60fps does matter. We've just all been taught that 60fps and sane use of CSS and the DOM (as currently standardized), so as to allow browser features to work properly, are mutually incompatible... which might be true. Using canvas certainly sucks for the reasons you describe; I wouldn't do it for more than a proof of concept. But long term, do we really need to hang the success the whole Web on the backs of some old and very ugly APIs? Can't someone come up with an alternative?
Exactly. This is a horrible misuse of the canvas element, alas, the moronic "war against native" destroyed all the good we had achieved ten years ago. I think then we had the golden age of web standards, progressive enhancement, graceful degradation, accessibility, and what not. Now we just have a race who can rape poor HTML/CSS/JS further.
* Copy/paste (holding on an article gives the options to email or report)
* Pinch to zoom
* Double tap to zoom (opens links instead)
* iOS swipe forwards and backwards (renders the page swipe animation twice, at 60fps I guess)
* iOS Reader View (go on, try it, I laughed)
And most importantly
* Any sort of accessibility
60fps doesn't matter to someone who can't see the screen.
60fps doesn't matter to someone who relies on assistive technologies to surf the web.
60fps doesn't really matter.