Personally I don't trust a NAS as far as I can throw it, or rather I'd use one the way I use Amazon S3.
My home server has a ZFS array, the media server and some other programs access it directly. If I want to move files to or from it I use SFTP. If I want to back files up to it I use rsync. I have Lightroom running pretty good on an external HDD, no way I'd take my chances running it on a NAS.
By "NAS" most people mean "box they bought from someone to share files on a network" - think Qnap or Synology. They'll call a "NAS" that is home-built a server, even if they do basically the same thing.
To make it more fun, you'll have people refer to "I don't have a NAS, I run FreeNAS on my server."
An appliance with the primary role of storage, and the ability to share files over the network are the distinguishing features for a NAS. Network support for iSCSI, SMB, NFS makes a NAS; sharing data exclusively over the media protocols (http, rtsp, etc) makes it a media server
