Earlier quoted context omitted.
According to Reddit's source code they're using a provider called Imgix - https://www.imgix.com/ - who I assume use S3.
Came across an incredible photo series of their dataserver. http://photos.imgix.com/building-a-graphics-card-for-the-int...
What advantages? If you're running these as headless servers, then what advantages does OSX possibly provide over cheaper, more powerful Linux boxes using e.g. ImageMagick (ok, ok, not having massive remote code execution vulnerabilities is one of them).