What sort of reason for "why?" are people looking for? The reserve was put in place as a safe bet to make sure Kinect and multitasking/snapping of apps worked smooth and didn't get in the way of the games. That's all there is to it, it's not magically 10% going to Kinect because it needs all that 10% to work, that's not how I read it, that's not how they talked about it either.
We've known about the change coming, it was said months ago, way in advance of any talks about introducing a SKU without Kinect in it. Removing the Kinect, as they've said, doesn't magically give you 10% overall GPU boost, so that's one thing that was reported wrong. EG's line is also off, I don't know who the heck they talked to, they don't list a name just some MS guy who replied, as if we've never had company dude A reply to a question with info that's wrong to some degree or fully, it's happened before.
Phils newest tweet posted above is clear about it, a reserve is now flexible and not fixed, but it's still there, there's still some amount going to the rest of the system, be it for Kinect + apps/snapping or just apps and snapping if there's no Kinect plug-ed in. What more questions do people have? Why did they take Kinect out? To drop the price, that's it, no other reason for it. I don't care what other type of PR spin YM might try to shine on it, it was business and nothing more, they needed an automatic drop in price, now, and fans wanted this option, so two birds with one stone.