The point about ECC and accepting lower error rates makes a lot of sense. It's the end-to-end principle again: since all of these HDDs are going into a global pool in which each of them is disposable and written content is protected by FEC spread across multiple drives, there is no need for each drive to spend a lot of resources, going deep into diminishing returns, trying to make itself as resilient as possible. If a network transmission fails, it is retried and doesn't need to be swathed in huge numbers of elaborate checksums and ultra-reliable links; if a hard drive fails, the content is recovered from the FEC and re-written out to a new drive.