Ex-enterprise gear or a retired or second-hand PC would indeed be easier on the wallet and able to do the job.
However, since I had neither, nor a way to get either...
And yes, Atom builds could handle NAS loads easily enough, no disagreement there; but add in the backups and other tasks, and you'll start reaching the limits of the platform. This isn't just a NAS box, this is the main server for the house.