Tom / KM,
There are quite a few associations that are licensed by the USGA to rate courses. Some areas of the country have strong women's associations in addition to the men's associations and the women like to rate their own sets of tees.
All ratings in Oregon have always been done by the OGA.
For years, here in Western PA, the Women's Golf Association of Western PA did rate the courses which were their members (just to private ones), but the WPGA did many of the courses in the area and when it was one that the women didn't do, we did the women's rating also. There are also the Keystone Public GA and the Erie District GA which rate courses. A couple of years ago, the WPGA and the WGAWP joined forces on ratings and we took their rating teams under our wing and we now rate all of our courses (and some that aren't members) for both genders.
As for the difference in ratings, the primary differences are in the distances the women are deemed to hit it (400 for two shots for the scratch and 280 for the bogey vs 470 and 370 for men) and the depth ratings for bunkers and rough.