Yeah, I was trying to point out you don't really need 3 copies of everything, and really 1 is enough for some stuff that's easy to replace. But the stuff that matters, you should have lots of copies of that. 2 backup disks is another way to go, just swap them, say, weekly. Photos from a once in a lifetime trip? make a bunch of copies, local and remote.
I'd counter this with what I do with my laptop. The OS is considerably smaller than the data I actually care about (<20gb), it takes almost no time to backup and so it leaves me with a very quick ability to restore the system to a known good state in the event of some kind of failure. I don't do constant backups of it, but maybe once a month i'll update the backup I have of the OS.