The new 'automatic unsubscribe' feature in FeedDemon is why web sites shouldn't have <link rel="alternate"> links to their main archive feeds from individual archive pages.
HubLog, for example, has RDF feeds of each individual post, including comments. This means that anyone reading a post can click the feed icon in their browser and be subscribed to that item straight away, with their aggregator taking care of automatically unsubscribing from the feed after a defined period of inactivity.
There is an argument that well-titled links to feeds can allow the user to choose which feed to subscribe to from a list of options (individual feeds, main archive feed, category feed, etc), but many of the browsers and browser extensions that automatically detect feed links don't offer that option.
Therefore, the icon for subscribing to a site's main index feed should only appear when viewing the main index page: in other words, the semantics of the link -- that it points to an "alternate" version of the current page -- should be maintained.