Reading the docs for HTTP::Headers I see this telling entry:

$h->title The title of the document. In libwww-perl this header will be initialized automatically from the <TITLE>...</TITLE> element of HTML documents. This header is no longer part of the HTTP standard.

I'm guessing the last sentence may be a key to understanding why these things are here. It might also be that many people just find them useful enough to want them as pseudo-headers.

Phil

Update: Fixed poor grammar.