I read that Ubuntu does not include Nvidia in their default install for philosophical reasons. Arch linux distributes Nvidia as a standard package. I remember spending several hours reading up on the Nvidia license issue when TC first started and we had our first Nvidia extension, and the debate boils down to being philosophical rather than legal. And basically our approach here is if it is legal to distribute then we distribute.
And here is the Linux part of the Nvidia license:
2.1.2 Linux/FreeBSD/OpenSolaris Exception. Notwithstanding the foregoing terms
of Section 2.1.1, SOFTWARE designed exclusively for use on the Linux or FreeBSD
operating systems, or other operating systems derived from the source code to
these operating systems, may be copied and redistributed, provided that the
binary files thereof are not modified in any way (except for unzipping of
compressed files).