My bad, i didn't express myself, for rendering framework i mean both the language and the technology that actually "execute" them. I understand that different browser do thing different but the concept are the same.

Also i don't know ios very well, but i have implemented complex layout in both android and the html/css/js and i can say that android is MUCH more frustrating, even when we consider browser backward compatibility, especialy on the animation side (css animations were a bit hard at first, but in little time i was able to construct complex animation very quickly).

I actually have builded a toolbar like the one on google docs (which i use daily) for editing data in a timeline for appointment, which had to be compatible with IE8 and while there was a lot of pain, i was able to iterate and experimentate a lot more quickly than android, and it wasn't that bad, also in my experience when we talk about layout and user interface there is A LOT more documentation on html/css than android, and there also are more framework/library that can help you deal with browser diffrence.