Regardless of the form factor (DSLR, P&S, Cell phone camera) the ONLY thing a higher megapixel count allows you to do is have a larger file, and in turn allow you to make a larger print or make a larger crop. Megapixel has absolutely NOTHING to do with image quality whatsoever.
5 years ago I was shooting events and products professionally with a 6.3MP DSLR (Digital Rebel) and if it was clear enough photo I could print a 20x30 with no image degradation. A little larger and there would be slight issues with the print if you get up close and shine a flashlight at the proper angle. I then upgraded to a 8.2 (30D) and it virtually made no difference. Same glass, same sensor size - same images. A later I upgraded to a 12.8 MP (5D) which let me print more 20x30s and even a little larger.
At the same time I spent more than I should have on a few L series lenses (which ultimately have paid for themselves) and they made the biggest difference in final image quality.
Manufacturers like to tout pixel count like it matters because it is easily quantifiable. They can say their camera is better than the other because the number is higher, but ultimately it's bunk. Seems like almost every market does it. Horsepower/fuel economy/energy savings/download speeds - we like numbers. Unfortunately the number for cameras doesn't matter.
I'm not saying the GNex camera is better for being lower, simply that it isn't worse for being lower. Image quality is a reflection of many independent factors, but ultimately megapixel count is not one of them.