Problem is that in the case of html, you generally lose the formatting information because that's not in the part you copied, but higher up or in a css file. So there is no native format, you don't want to copy raw html code into a word processor, nor the plain text, but something that more or less looks like what you copied. Not to mention that usually the selected part is "broken" html because not all tags are closed. So it's not that simple and I don't think it's safe to get rid of the list support.
For images and other data formats with an obvious raw format are much easier and better suited for automatic convertion. That can be done automatically without changing the API.