Do they specify the VMs tested? AWS has a lot of different versions of things in play and most of the people I know fall into two camps: fairly generic VMs running compute jobs, which probably would compress well, and VMs running huge databases / image farms / etc. which do not. By VM count I'm sure the former dominate but by total storage consumption I think the latter wins – I would, of course, love to see if anyone has hard data.

AWS doesn't have that many OS versions. Besides I'd expect huge datasets go either to S3 or to ephemeral storage like Cassandra clusters etc. EBS isn't the best place for it. Your mileage may vary etc.