Entirely unsubstantiated and speculative, but I'm not alone in that speculation.
Do we know that Nikon are not doing this before they write the RAW data? It's possible for example that the in-camera processing engine wouldn't be powerful enough. I don't know.
There is no reason to think that Nikon does it but Canon doesn't.
What we have for the P6000 is very easy. The people in charge of the coolpix line of product simply think that nobody will be able to handle the noise of the Sony sensor better than themselves.
The problem is internal, they should have let the DSLR guys draw the spec of the P6000 instead of letting the coolpix team do it.
Besides, let's not forget that as a whole, the Nikon mgt has finally become very aware of the importance of noise. I wouldn't be surprised if an exec level decision had been taken to prevent the release of noisy raw files in the wild. They must have thought that it would damage the image of Nikon as a whole.
Not knowing how noisy the files from this 13.5 MP snesor are, nobody here can really assess how wrong that decision was...
Now, let's be a bit realistic here. Nobody will use this coolpix for real critical applications where a 10% better noise handling would make a significant difference. So the possible pre-processing of the raw file by Nikon is not sucha huge problem in itself.
The reliance on Windows is a real pain for people like me using a Mac, but I could of course use my VMWare fusion instance of Vista to solve this problem in a heartbeat. So beyond the emotional response, there are solutions for most of us.
Now, I will probably no buy a P6000 but will instead use that money to buy half a video enabled D90 anyway.
As a side note, the piece of gear that contributed most to enhancing my experience as a photographer recently is the pair of Nuforce Icon-S-1 speakers I equiped my Mac Pro with. These babies sound almost as good as my 4000 US$ B&W 804s speakers. Unbelieveable. Let's focus on what works.