There is a place for large MP and there is a place for small.
I bought Nikon because 12Mp was enough for me and is actually better in low light. I have no trouble printing up to A3 size, and I am very unlikely to need anything this big. Most of my shots are of people and will be viewed on screen at screen size, or printed up to maybe A4. I shoot 14bit RAW and delete all of the pics i take that don't make the grade. I still have a more than 100 GB worth of files after less a year.
There is a need for large format for people who NEED large format. People who print cosmetic posters for "drug stores", billboards, train advertising etc. If you dont do these things, you dont need anything more than the D3x.
If one "needs" high MP's, there is always the new Phase One IQ180, 80 MP back. It goes for a paltry $44,000 not including the camera, or a lens.
As my income over the past two years has rapidly traveled south, I plan on buying a 4x5 Field camera. A good used one may well cost half of what I paid for my D700, 14-24mm lens, and assorted other accessories. Technology is great, but it does come at a high cost.