I think this has more to do with manufacturing consistency than anything else. If a hard drive fails in a few weeks than it's quite likely the lot it came from is also likely to fail.
Unless something fundamental has changed about hard drives I think my point is still correct. Hard drives are electromechanical devices that also wear; bearings wear, fluids evaporate, and heads hit the platter. They spontaneously fail like light bulbs spontaneously fail. It's not spontaneous at all. If you know a light bulb is about to blow or is near the end of it's life cycle you change it.
In the greater scheme of things the cost of the hardware is miniscule compared to the data on it. If drives start randomly blowing up in your face it's time to get a different model.
What I'm getting at is we put more care into the maintenance of our cars than we do our data. If you think hard drives are expensive than what do you think of the cost of productivity while an office full of people wait for a RAID to rebuild. Instead of waiting for the inevitable failure wouldn't it be better to cycle old drives on a friday evening when usage is low.
RAID6 is just a bandaid on a bandaid. It came about because drives are of the same age when a RAID is built. And start failing around the same time. RAID 5 can recover from one failed drive, RAID6 can do 2. But you are still vulnerable if a 3rd. But this is still reactive thinking, "I will replace them as they fail", rather than using proactive solutions.