- can' t backup remotely through ssh and rsync

I don't personally run rsync-over-ssh, as my backup NAS is local so there is no need to encrypt the backup flow.  In that scenario you do need to run rsync as a daemon/server.

I've always assumed that you also need to set it up that way when you are running rsync-over-ssh.  Meaning that the rsync protocol is just being tunnelled over the ssh transport by the NAS (and that Netgear is not executing remote shell commands over ssh as your links describe).    The method I am envisioning is outlined in method 3 in this old blog post: http://toddharris.net/blog/2005/10/23/rsyncing-through-an-ssh-tunnel/.

Though I could be wrong about this, it would be the simplest approach for Netgear - since they could simply "bolt on" the tunnelling transport to their existing code for rsync backup jobs, and not create a completely new option.  Also, AFAIK you do need to enable rsync as a service on the remote NAS when you are setting up rsync-over-ssh backups between two ReadyNAS.  If they were running remote shell commands, you wouldn't need to do that.