Almost every animation/image there suffers from horrible moiré because a normal browser canvas was not meant for this. Fine line art needs supersampling and high quality filtering.
You're complaining about a small subset of "dweets" there. There are thousands of great visuals there that are not "fine line art" and do not suffer from what you described. And no, I do not think it "needs a better renderer" as high quality "rendering" is not the point of dwitter.net, the point is producing amazing things in 140 characters of javascript.
Almost every animation/image there suffers from horrible moiré because a normal browser canvas was not meant for this. Fine line art needs supersampling and high quality filtering.