Quoted from here
For that extra $50 I can save $250 buying NAS adapters, sounds like a STEAL.
At $179, this is the least expensive Extreme Base Station yet, but its still more expensive than similar products from manufacturers such as Linksys and Belkin, whose 802.11n wireless routers start at around $120. However, these basic models are lacking many of the features offered by the new AirPort Extreme Base Station, such as shared-printer and NAS support. Once you move up to products that offers similar features, such as Linksyss WRT350N, prices are roughly comparable (and, if Apples claims are true, the Base Station will be easier to set up and administer).
For that extra $50 I can save $250 buying NAS adapters, sounds like a STEAL.