That is not what I've heard. I've read that the problem came from some kind of inside finish or tape that kind of dampened the mirror. This tape started flaking and did get stuck between shutter blades. Now before they realized what this had caused, they started cleaning and replacing this tape, but... there were still some pieces of "stuff" between shutter blades and the dust (particles) were getting back on the other side of the shutter after some actuations. This is why I think the phenomena was amplified by those who were shooting high frame per second burst often. The mirror flapping was just shoveling the stuff back.
A Canadian Nikon rep told me that the shutter blades that are used in the D610 is basically the same as the one in the D600. Having known this person for a while, I'm inclined to believe him.
Now, problems to arise with any human made things. We've had bridge collapsing, Nuclear plants go bezerk, all kinds of problems and recalls with cars, so we should keep a little bit of perspective with this one. But, this didn't excuse Nikon Service Centers to treat their customers the way they did. On this last point, they are 125% wrong all the way.