Re: there but for the grace of God...
"Nothing to do with SATA and everything to do with size."
No, it's far more to do with SATA than the size - the RAID set size is only a linear relationship to risk of failure. The hard Bit Error Rates (BER) on SATA disks are far higher than on Fibre Channel, SAS, or SSD disks. Therefore the chances of a hard error during a RAID set rebuild are much much higher.
"even RAID6 is not good enough once you get past 10TB"
Nope - again wrong - RAID 6 will last you reasonably safely well past that. So for instance RAID 6 would be fine for most uses for 4TB disks in a set of 14:2. Which gives a per RAID set size of 64TB including parity... Which would have a hard failure probability rate over ten year of 0.03304 % or better.
(MTBF): Manufacturer Spec, Enterprise (1.2M)
Non recoverable Error Rate (SATA) : 10^15
Drive Capacity: 4TB
Sector Size: 4KB
Quantity of Disks: 16
Volume Rebuild Speed (MB/s): 15MB/S