Mel,
There are 2 possible reasons that they are not on the NCI list: 1. They didn't apply (most likely) or, 2. they didn't meet the criteria.
It's a whole lot pf paperwork and basically funds research only - not patient care, and is basically a grant process. See:
http://www3.cancer.gov/cancercenters/CCSG_Guide12_04.pdf None the less, being one of the 20 NCCN member Institutions packs a lot of weight anyway. Stanford is at the cutting edge of cancer research and patient care. The NCI institutions follow the guidelines developed at Stanford and the other NCCN member institutions.
I think Leslie explained the "comprehensive" part pretty well.