I can't answer your overarching question, but the majority of Feed Digest's user...

petercooper on July 31, 2010 | parent | context | favorite | on: Three years ago, I sold my startup because I was a...

I can't answer your overarching question, but the majority of Feed Digest's users were merely processing snd republishing feeds to HTML includes for their sites rather than actually subscribing to or using the RSS output features. Think RSS-to-HTML (or JavaScript.)