Why would you even say that? It makes no business sense for them to disallow competitors with their eventual SDK because they will still be selling much more expensive hardware to those people.

With an SDK they can only sell more products, whether that is apps, hardware, or both.

Where they should limit their SDK use is in branding — they probably wouldn't want poor quality or badly designed apps advertising (or even using) the Pencil SDK. It would reflect badly on their product. So they need to maintain control in those cases.

They shouldn't allow "any kind of app." They should allow "any kind of app that meets their standards for quality."