I agree that what the article misses is that Backblaze is spending the money on software rather than hardware, since the price difference is so huge (and the software solution is a fixed cost).

What I'm more interested in is whether the lower MTBF of the cheap drives and home-brewed chassis ends up with a higher cost per year due to higher failure rates. If a desktop drive costs $100 and fails three times a year, but a server drive costs $200 and fails once every 2, the initial cost savings is moot.