I backup to Glacier as well. For me to need to pull from it (and pay that $90/TB or so) means I've lost more than two drives in a historically very reliable RAIDZ2 pool, or lost my NAS entirely.
I'll pay $90/TB over unknown $$$$ for a data recovery from burned/flooded/fried/failed disks.
And let's be honest. If the house burns down, the computers are the third thing I get out of there after the wife and the dog. My external backup is peace of mind, nothing more. I don't ever expect to need it in my lifetime.
I'm not saying its a bad deal, I very much wish I'd gone with deep archive (especially with the recent addition of "update if different" to the API)
With 10TB drives being available for $80-ish... I expect a lot of semi savy people to upload tens of terabytes then cry when they see the bill.
Numbers rounded a bit for simplicity.