This is a HTML problem/question, not a HTTP one. Well, the essence of the original question, if put to a broader context was: "How do I split on line boundaries, when I don't know which line ending schema is used". This for itself makes a quite interesting problem, IMHO.
And in this context, it's not irrelevant what the endings are, even if I'd agree that it's not important from HTTP's idea of a HTML body (ah.. which it does not care about at all, it's a transpher protocol that does (of course) not alter nor interpret any message content.)
Should you, however, do any processing of HTML data, you need to worry about line endings -- at least when a pre tag is involved... Just because a broser can simply strip the document from any line endings (outside of pre-tags), other application should not. A browser won't output anything. It's the end of the road, so it needs not worry about a documents internal integrity.. ;)