You forgot Feedburner that Google used to monetized feeds. Almost all bloggers I followed in Google Reader used it to track and monetize. Google had a lot of control over RSS.
I don't know how it is know but when I was doing a lot of SEO publishing 10 years ago Feedburner was the best kept secret.
People would always be complaining that Google wouldn't index their pages for months but if you: (1) burn an RSS feed, (2) subscribe to the burned feed, and (3) add items to the feed, the items would be indexed almost immediately.
People would always be complaining that Google wouldn't index their pages for months but if you: (1) burn an RSS feed, (2) subscribe to the burned feed, and (3) add items to the feed, the items would be indexed almost immediately.