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]
Erm, you guys covered this already New Xbox 360 Motherboard Leaked, Has 256MB Flash Memory.
Anyways, I assume that the added memory will simply be used to store the NXE and you won't have access to it, however I don't understand why new console's won't just have the NXE preloaded in whatever memory the original guide was on.