Or ReadyNAS, but I suppose only with their modified XRAID2. I thought QNAP and Synology also had something similar, so I guess I take it for granted that everyone is running this type of setup.

So, with a hybrid setup two drives need to be replaced and with a standard RAID5 setup, all disks need to be replaced. However, with standard RAID 5, don't you also have to create a new volume within the new space? In other words, you can't expand the original volume without rebuilding everything (which would require a backup and reformat).

Even with ReadyNAS XRAID2 (latest version) there are still caveats - the replacement drives need to be larger than the largest drives already in the system for expansion. Not so with Drobo. Then again, Drobo is like a time-bomb...