So if we go back to that Eurogamer interview, this is precisely what they say about using the traditional controller, hopefully explaining why they will release it
Digital Foundry: Let's talk for a moment about the Navigation Controller. Is that effectively a redesigned, pared-down DualShock? Does it add any kind of additional motion control to the system?
Richard Marks: No, it is exactly the left "hand" of the DualShock. And it's not necessary. You can always use the DualShock instead of the sub-controller.
Digital Foundry: But that would be a bit of a handful on a game like SOCOM...
Richard Marks: I found that if you're sitting down and it's on your knee, it's not a problem at all, it feels pretty natural. But if you want to stand up and you want a user-friendly game then you use the sub-controller.