Why will I pay so much for a NAS enclosure, when I can buy one with HD

Hi All,

Looking for a storage/backup device. I have an older DELL, maybe make a file share system, but think I want RAID array.

Looking around, I can find enclosures like this: http://www.newegg.com/Product/Prod [...] 6822155009,
but for a little over $100 more I can get this: http://www.newegg.com/Product/Prod [...] 6822204072, which includes 2 TB of disk.

What am I missing here? No way can I buy 2 TB of storage for the $120 difference in price.

Do you buy the external enclosure because you already have drives you want to put in it?

Thanks for any help.

PS. Might be just as wise to buy an external drive for backup. I am not (yet) into streaming content from a NAS to a HTPC, though I don't know if a NAS would work with my Logitech SqueezeBox. If it would, that would be a big incentive to do the NAS rather than an external drive.