Originally Posted by awx
Also the absence of them does not preclude a chapter start. They just aren't suitable for this purpose.
I agree that authors should use them at the top of pages where appropriate but that's really up to them.
In 99% of the books I have read they do exactly that. They mark the beginning of a chapter and a chapter start is never presented without them. The ePUB standard expects them and CSS also works well with them. They are not just dressing for the top of the page. They are the structure for the ePUB format.