NAS vs Shared Enclosure

[unifyzero]

Is there any reason to use a NAS rather than a multiple bay hard drive enclosure shared over a wireless router for backing up computers and sharing files?

More specifically:
I'm looking get a 4 bay NAS or enclosure and use it for backing up computers as well as storing/sharing media. Going off of TigerDirect I can get an enclosure for $150 less than a NAS. Both are SATA, 3.5", and include hardware RAID 0,1, and 5. The NAS supports PCless torrent downloading, and appears to be able to backup USB devices simply by plugging them in and pushing a button (I doubt I would use either feature enough to justify $150). My wireless router supports USB file sharing, so I could simply hook the enclosure to it and share it in that manner.

Does a NAS offer anything to justify the $150 difference?

EDIT:
So I understand that a NAS will provide it's own file system while an enclosure does not. What sort of pros/cons come along with that?

 

[FireWire2]

Does your system on 24/7?
If so the DAS (Direct Attached Storage) would do just fine

 

[Guest]

Not really, but your decision will be based on the features you need. Newer routers with USB ports and sharing are *almost* as good as a dedicated consumer-grade NAS device. I've gotten a lot of utility out of an NSLU2 over the last 4 years, so much so that a few customers have had me set one up for them in their homes. The NSLU2 is getting ever-harder to find, but the Linksys routers of late that have USB ports for sharing provide virtually identical utility to their NSLU2.

 

[unifyzero]

Thanks for that. More and more I'm leaning to an enclosure shared over router, or maybe going with a custom NAS/Server. Still looking into pros/cons of each path