This is a question asked in a blog comment by David Eppstein.
Is there a reason for not having a “link rel=alternate” pointer to the feed? Yes, there’s a “Subscribe via RSS” link on the page, visible to humans, but the link rel syntax allows software to figure out where the feed is given only the url to the blog itself.
I don't know the answer. Could someone clarify this, please, and add the feature if appropriate?