Terminology. I just like things having the right names, and a full-on computer that just happens to be spending its life providing storage for other users on the network is a file server, and has been called such for a long, long time before manufacturers invented very specialised boxes called SAN and NAS.
I wonder, too, why the domestic user should ever require a file server or an NAS. Cynically, I think that, like a DAC, it has become a must-have, and the market will always rush to encourage and fulfil such things
Uncynically, in partial answer to myself, I reply that the user who has ripped a large CD collection, let alone a DVD collection, probably has more data than my ex-employer collected in their accounting and business databases over a decade. I also reflect that the streaming of a single movie from one device to another involves a huge amount of data, the delivery of which is very time-critical. Domestic users who want a NAS for their media collection, tell me that the reason is that they want a small box, that runs cool, draws little power, and needs no monitor etc, and they do not want to keep their PC powered up --- which is fair enough: they want a NAS, not a file server. I don't know how much they save with their NAS's: My PC, which does everything, is about the same spec as your last mentioned machine and draws as little as 120 watts with a 22-inch monitor.
Then again, some tell me that they need a NAS, because they simply want to share music and general files. They seem not to have noticed that even Windows will do that.
It's just the view of an old-fashioned sysadmin and IT manager that dogs are called dogs, cats are called cats, and neat little boxes that contain a pile of disks and do nothing but read and write them are called NAS --- big boxes that could do anything you throw at them, are called file servers.
Does it really matter? To me, yes, or I wouldn't be wasting my time writing this. To anybody else, particularly outside the IT industry? probably not...
I quibble. Sincerely, good luck with your machines.