Dust is a common fact of life on digital SLR cameras. The only alternative is a point and shoot with a sealed body. If you look close enough, you'll find dust on every sensor. Mike Hagan's recent blog post showed dust on every camera he owns.
We spend a lot of time talking about cleaning the sensor, but in the mirror box you also have a moving mirror that fans air - and dust. You also have a relatively large mirror box with lots of nooks and crevices. The mirror box can't help but collect and hold dust - and almost nobody does anything beyond briefly using a blower on the mirror box.
The FX sensor has more than twice the surface area of a DX camera. With the high pixel count of the D600 and D800, you have twice the resolution as well - and generally we are looking at dust at 50-100% zoomed.
The D4, D3, D2 etc still have dust. But in general the pro market is used to cleaning dust on a sensor and the relative number of complaints is small. So you have a large group moving to high resolution FX sensors for the first time, and they are not tolerant of dust and are not practiced at cleaning it off the sensor.
A quick cleaning with a blower is enough to clean 80% of the dust or more. Sometimes a blower needs to be used more than once. But a blower alone is probably enough for most photographers. A brush or wet cleaning is only done occasionally - a blower is normally enough.
There may be more dust on the D600 than earlier cameras, but there are a lot of sources of dust and more attention today than it has had since the D70.