AD is the 800 Lbs gorilla from what I've seen. I've been looking for a job for over a year and have seen a 10 to 1 ratio of AD to *nix jobs and at least a 50 to 1 ration of AD to Novell jobs. You can say Novell has so many licenses and all that but the real world just doesn't support your argument.
The point of the article was that the Linux community has not made a good enough effort to comingle with AD based on ADs popularity. Novell eDirectory is not really from the Linux community and it isn't free either. It may be a viable alternative but it isn't from the Linux community.
Put on your IT Director or CIO hat (if YOU can imagine ever attaining such a position) at think about how many vendors you want to manage. Obviously, you want interoperability between the various OSes you run and it would be great if you can reduce costs by reducing the amount of admin overhead. Now someone suggests adding in Novell or IBM products to make MS, Linux, and Unix all play nice. Great, now you have to hire another skillset to make it all work and cross train your existing admins... Doesn't jump out as a huge money saver does it.