Native Instruments just released an 88-key version of the Komplete Kontrol keyboard. Right after I got the 61-key version, of course... :P
While there are certain elements you can make NKS-ready, for full integration it needs to be a Kontakt Player library. That way, for example, you can press the "browse" button on the keyboard, and the library will appear along with all of the different snapshot presets to navigate through. It's really convenient to be able to tweak effects and settings using the knobs while playing, or press the arrow buttons to advance through the different presets.
So the main reason for the upgrade price was due to licensing the Kontakt Player. Otherwise we prefer to keep updates free. Any discounts will apply to the upgrade price, though. For example, you could redeem your Orange Slices points... though those will save you a lot more on something with a larger price tag--it'd be a pity to redeem your 50% off discount to save $10. ;)