When we say server, we usually mean computers with these safeguards in place. Whether or not you want P2P or a server is a different issue.
I know people like to use personal experience to indicate they've never had issues without all these safeguards. Congratulations, you're one of the lucky ones. While I personally have also been as lucky with my computers, I know many others who have not been as lucky. I'm sure if you search through the archives you'll find similar stories of disastrous crashes.
That complexity argument about server parts is frankly bogus.
If you can put a piece of bread in a toaster, you can swap a hard drive in a hotswap case. Same holds true for redundant power supplies.
If you were on on a desktop, your hard drive fails what now. Open up that computer replace the hard drive and restore your backup assuming you have a full system backup. If you don't, you have to reformat, install drivers, updates, and programs. That takes several hours. Unlike your buddy up there with the hotswap bay, you have to be familiar with opening up the case, switching out the hard drive, changing the boot order, installing windows from scratch, finding drivers, etc. He just pulls out the bad drive and slides in a new one in an easy access hotswap bay.
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