My issue is that they were comparing on-line hard drive backup to off-line bluray but with an expensive and fancy robot system. Which is not quite a "fair" comparison. The Bluray drives also have to be connected and use power. The robot uses power. A spun down stand-by hard drive uses only about 0.75 watts! That means you could have half a PETABYTE of ONLINE storage for about the power of a single traditional lightbulb.
At the rate hard drive density keeps going up, it seems optical storage just can't keep up. We have seen this happen with CD, then DVD, and now bluray. Doesn't help that the prices on bluray discs were kept way too high for far too long.
Hard drives are now 4TB for $150! Bluray is still around $1/disc for quality, but each is just 25GB. That means you need 160 discs to equal one hard drive that costs slightly less, writes and reads a hell of a lot faster, and actually takes up considerably less space.
I am not saying hard drives for backups is ideal in all cases, but it certainly is a much more attractive option in many ways.