That caught my eye too, and I guessed on Twitter that it might be a typo/under-e...

		thesethings on Feb 13, 2012 \| parent \| context \| favorite \| on: Tumblr Architecture - 15B Page Views a Month and H... That caught my eye too, and I guessed on Twitter that it might be a typo/under-explained. Somebody from Tumblr (though on a different team) was nice enough to respond and guessed that it was because all media on S3 was not counted. https://twitter.com/#!/adamlaiacano/status/16914079173274009...

Thanks. It seemed completely unreasonable to me until I saw this explanation.