User blog comment:Mathmagician/Project - Individual Pages/@comment-1863391-20120112231530/@comment-4674838-20120114005249

Yes. Disambiguation pages should not have categories. (I don't know if you ever use disambigs on wikipedia, but if you do, you'll notice they don't have categories.)

It's mostly a nit-picky editorial standards thing. The only concrete reason for it really so far as I know is so that people will find actual content pages when they search by categories, rather than finding disambiguation pages. (Why click 2 links, 1 to get to the disambig and 2nd to get to the content page... when you can just click the link for the content page in the first place?)