Note: Shacknews apologizes if you're getting tired of these stories that point out what PS4 can do that Xbox One cannot.
PlayStation 4 will support user-replaceable hard drives. According to Sony's Shuhei Yoshida, hard drives are upgradeable "like PS3." PS3 used standard notebook hard drives which could be swapped rather easily. Xbox 360, on the other hand, relied on proprietary hard drives for a bulk of the console's life.
PS4 will launch with a 500GB hard drive, but should that not be enough, you can simply buy a larger one. (Terabyte drives go for well under $100.)
Xbox One does not support user-replaceable hard drives. However, that console does support external USB 3.0 storage devices.