Microsoft has confirmed that it's newest Xbox 360 Arcades come with 256MB of internal storage, making it NXE-compliant without you having to buy an extra memory card. Old Xbox 360 Arcade owners are still out of luck though.
A Microsoft spokesperson told Xbox360 Fanboy that they constantly update the console's 1700 plus internal components and that the Xbox 360 Arcade was moving to internal memory. New buyers (of which there were many) can download content and save games right out of the box. Old users... well, you probably already got the external memory anyway, right? Not like you could return it now. Try not to get too hung up on buyer's remorse. [Xbox360 Fanboy]