I agree, hard to understand the changes. Actually fond some addition info as I was writing this though. http://sortbenchmark.org/
Old record was 330 r3.4xlarge machines. Which actually cost very similar today. It looks like the old record used a LOT more RAM than this one. 40,260GB vs 3,152GB and similar CPU 5,280 vs 4,728 cores. Although having the RAM doesn't mean it was used, but unless they were using all the RAM I don't see why they would use the more expensive r3 instances.
Edit: Follow on, I think the cost savings is definitely in the low RAM usage. Can't really get that many cores without more than 3 times as much RAM in AWS.
Old record was 330 r3.4xlarge machines. Which actually cost very similar today. It looks like the old record used a LOT more RAM than this one. 40,260GB vs 3,152GB and similar CPU 5,280 vs 4,728 cores. Although having the RAM doesn't mean it was used, but unless they were using all the RAM I don't see why they would use the more expensive r3 instances.
Edit: Follow on, I think the cost savings is definitely in the low RAM usage. Can't really get that many cores without more than 3 times as much RAM in AWS.