There is a difference in the firmware and how the drive handles speeding up and down. NAS drives are spinning 24/7/365, they only spin up or down during restarts of the SP. Regular drives on the other hand will attempt to save power by spinning up / down on demand. This can cause lifetime reliability issues as the drive experiences the most stress when it's spinning up. Also there can be thermal considerations, regular drives know that they are primarily accessed in bursts and won't be expected to go 24/7/365, so they don't vent heat as well. NAS drives are expected to be rotating all the time and have better sustained thermal design.
I built my own NAS using FreeNAS and common parts off newegg/amazon. I made the mistake on my first array of using 7200RPM desktop performance drives. Ended up being a nightmare with thermals and I then swapped them for 5400RPM power saving drives, worked for awhile but then started having all sorts of problems. Finally bit the bullet and switched to 4x4TB WD Red 5400 and haven't had any problems in years. This system not only does typical CIFS shares for the house, but also iSCSI volumes for my ESXI system where I do lab work.