Agreed. And for my server, I have two spare RAID controllers, two spare 3-bay hot-swap cages, and several spare drives, including a sixth drive already running in a 5-drive array as a hot spare.
But RAID is a bit unusual in that it's explicitly designed to withstand that type of failure. Indeed, maximising uptime is the point. Most PC builds aren't like that though, and being "prepared" is, in itself, quite expensive.
Of course, if we were really prepared, we'd have a duplicate and duplexed/mirrored server running.