“Yes. The more our customers use their profile and download digital content, the larger the file size necessary to store that content and move it between consoles gets. Therefore we increased the size of the memory to enable our customers to take more of their Xbox profile with them on the go.”
So there you go. Seems a bit small compared to the Wii U's ability to connect to any size hard drive they want, but an increase is still an increase. Perhaps the Xbox 720 will offer us a different stance.