Sorry M$, I call bullshit. See you have a limited number of resources (we'll call that X) dedicated right now towards "hardcore" (cough cough 12 year olds playing the same shooters with different skins 90% of the time and a good game here or there) game production and no resources at present dedicated towards "casual gamers" (Your mum, your dad and your 20 something sister). We'll call those resources (or at present, lack of them) Y.
X and Y are drawn from the same pool of resources, which is M$'s net profit. We'll call that $.
We assume $ is not infinite (since by definition it can't be). Just to better illustrate the point we'll divide cash up into arbitrary units. Let's say that M$ has 100 units of $ at their disposal.
Further, we have to assume the following is true:
100$ = X + Y
Since Y was effectively set at 0 until Natal development began, the following must also be true:
X>Y
If Y=0 then X=100$
Now from that same resource pool ($100) M$ is claiming they'll increase Y without effecting X.
If Y>0$ then X<100$
It could be as little as Y=1$ and X=$99, but their claim is inconsistent as any resources added to casual gaming (Y) must be taken from their available resources($) which means that hardcore game development funds (X) must be decreased.
P.S. I like word problems and I've just had my second cup of coffee. I could have explained it better or differently, but I didn't. So what?