He meant that if EBS has the same issue as his Exchange servers. To explain in more detail: You have 10TB disk space with 10.000 IOPS, your users buy 4TB with 10.000 IOPS then you have 6TB of storage wasted.
If Amazon has that problem with EBS, then selling that storage capacity as Glacier and using just the idle IOPS (or leaving a small bit reserved) allows them to sell capacity that would otherwise just be useless.
That's the point. They aren't trying to sell IO with glacier, since they've already saturated that with EBS. They just want to sell the spare storage capacity, ideally in a write once read never use case. That way they can achieve 100% utilization out of the drives.
So if you use a lot of IO with Glacier, they are going to charge you like crazy, since you're potentially impacting EBS customers.
I'm that guy. I should update the post; Amazon "fixed" the retrieval fees in late 2016 and I would've paid less than a dollar had the current pricing scheme been in effect when I did the retrieval.
If Amazon has that problem with EBS, then selling that storage capacity as Glacier and using just the idle IOPS (or leaving a small bit reserved) allows them to sell capacity that would otherwise just be useless.