actually, i think the author does understand this and in the case of stackoverflow, i think he's obliquely making the case that many of the effects could otherwise be achieved with css without creating the performance and memory hits you might get from using $().

in most cases, js performance is a non issue, but when it is, it's interesting to see how and where you can optimize, which is really what his add-on (again, obliquely the real point of the post) seems to target.