New Nikon 24mp sensor (D5200) is made by.... Toshiba! New kid on the block?

It could very well just be the product of a simple bidding war between sensor manufacturers.  When trying to reverse engineer these things, it's almost always wise to follow the money.  It just might be as simple as that.

I'm just saying the ability to squeeze a competitor, who also happens to manufacture many of the sensors they use, isn't necessarily a bad thing for Nikon.  But it doesn't benefit Sony.  You might argue that they don't compete on the SLR front from a sales perspective, but a fight is definitely taking place in mirrorless.  If you're Nikon I would think it doesn't behoove you to become completely dependent on sensors manufactured by an adversary; how much of that was a factor in the decision we will probably never know.  Companies can be selective and don't have to award to the lowest bidder, either... it's anybody's guess.

As far as Sony providing all their sensors to others vs keeping the "best" for themselves, I don't think that's plausible.  I just don't see them in a position (financially or otherwise) to play any kind of zero sum game here.  They're not the only game in town, other manufacturers out there are around to fill the void if they get arrogant.  It is still better to have a piece of everything (Nikon's sales) vs. all of nothing.