[olliej]

Yeah I agree with almost all of this - the massive size and complexity of commercial engines makes it seem like JS the language must also be complex.

I also agree with the idea that these sites will probably be able to/want to create JS that breaks these small/lightweight engines requiring constant work :-/

This final point I disagree with entirely. You can't point to Bellard doing something as evidence that it's reasonable. This is a guy that wrote a program that generated a TV signal via a VGA card. :D