Depends on wether you make the distinction between "backup", as in spare copy, and "archive", as in dump
But you're quite right, even a RAID array is as a whole a single point of failure (controller, file system etc) and shouldn't be relied on on its own - although it does address the most failure prone part of the chain, the hard drives.
One tip for the thread starter: don't get all your drives in one place, or at least ask the vendor to send you drives from different batches. If the drives making up a RAID array are all from the same batch, chances are if one fails it might not be alone, resulting in loss of the array. Was quite close to this cataclysmic type of event last week when two drives failed within 3 hours of eachother on a RAID6 array. I tend to mix even different *brands* of hard drives for a new array these days, as long as they're the same size and speed it doesn't matter.