Hi,
My _guess_ is that Nikon is closed source so that it won't be hacked.
IOW, they don't want folks to mess with it. If people poke around with the firmware, things will likely go wrong and a blame game will pursue, and while one might _say_, well it's at you're on risk, if the camera is in warranty, if it doesn't work, who'll fix it if it doesn't work?
That is probably the reason that Panasonic 'de-hacked' the GH2.
It would make sense to me to make the sources for firmware open and at the least make the cameras user 'fixable', but that would take a lot of doing, perhaps more than a little. I'm suggesting that users would have to know how to push software into their camera, at least be able to read instructions. And that might be hard.
I'm all for it. But I don't expect it to happen anytime soon.
My best,
Mike