This doesn't make financial sense. nVidia don't care about 590 sales, they care that they have the fastest single processor graphics card and the fastest dual processor graphics card around.
It would make no sense for them to try to push a few extra sales of the 590, which is such a tiny part of their revenue.
Would I believe that they are doing something underhand to favour their cards over AMDs? Yes, I would. But for them to push the 590 and only the 590 is just stupid.
So if the rumour is slightly wrong and that nVidia have asked/paid/whatever for it to be delayed so that they can work with Crytek in order to optimise their drivers to blow AMD drivers out of the water... I could believe that.