RAID 5 is good at losing a second disk soon after the first, even with a hot spare (which means you lose the array). I think the GP meant something like "RAID 6 should be the bare minimum", or perhaps "any level of RAID is not as good as having an independent backup system".
But I'd like to know what they actually meant, too.
DRM and keys prevent you from using your version of the software on that device. It does you no good to be able to change it if you can't use the changes. The developers have decided they don't like that idea, and GPL 3 ensures that anyone who wants to lock their device down like that will have to use some other software, instead of taking something open source and locking it down too.
There's nothing to stop Apple or anyone else from implementing something compatible; it just can't be the same code.