D600 : Why cripple live view?

I was hot to see the specs on this D600 camera. Looks great!

Can anyone please explain to me why you can't change aperture in live view with real-time simulation? It's bad enough that you have to open up the aperture anyways for critical focusing.

Is this a physical limitation or just crippling code?

Why do even the low-end Canon rebels allow this functionality? Is the physical design less limiting?

Nikon seems so intent on giving feature rich cameras at a low cost, but why do they seem to always cripple this feature?

I truly want to know the reason behind this strange omission, which honestly is holding me back from getting one of these cameras in the future. I focus and expose with live view 80+% of the time for landscape work.