Makes sense. I still think it would be cheaper to just reload it from S3 (straight into memory, not using EBS at all) on every boot. The entire OS shouldn't be more than a gigabyte which is quite fast to download as a bulk transfer straight into RAM.
Yes it would be cheaper, but the whole point of this article is trading off cost for faster boot times. They address your points in the article, how it's faster to boot off a warm EBS instead of loading from scratch.
