Nitrogen in tires?

[Low Note]

Has anyone in this forum had any experience with nitrogen in their X6 or even X5 run flat tires? I had it in my recently sold Mercedes E class with regular Continental tires, and it worked very well with virtually no change in pressure between warm and cold climates. But I've never had run flats before, and am going to be getting them (whether I want them or not...probably 3rd generation Bridgestone all season) on my new X6 which is currently in production. One would assume that nitrogen would work as well in rft's as in non-rft's, except for the fact that BMW has publicly stated that they do not endorse the use of nitrogen with their vehicles. Since nitrogen is a larger molecule than regular air, does not seep out of the tire as easily, and does not change very much between warm and cold climates, why would they suggest that nitrogen should not be used? Any helpful comments would be greatly appreciated.