http://www.slideshare.net/AmazonWebServices/building-scalabl...
Are there strategical interests to not have a symmetric link?
Geographically its relatively close to Singapore (compared to other data centers anyway), all of the cables from the eastern side of the country either go up to Japan via Guam or go to the US via Hawaii. Its not uncommon to see a route from Sydney to Singapore go through the US, and/or Japan before reaching Singapore.
"The US Standard Region automatically routes requests to facilities in Northern Virginia or the Pacific Northwest using network maps." http://aws.amazon.com/s3/
Edit: that's be s3-external-1.amazonaws.com for us-east and s3-external-2.amazonaws.com for the PNW. See https://forums.aws.amazon.com/message.jspa?messageID=185820