One thing the Pathfinder campaign world has going for it, is that it is made up of a huge amount of unique areas, each which could serve as a campaign world in its own right. Each has a different feel, from gothic/horror, political intrigue, science-fantasy, indiana jones-ish, lost world, asian fantasy, etc.
This means that every suppliment can contain a huge amount of interesting and new material and rules that still works with everything else. And if the current area's hook doesn't grab you, come back in a couple months when they move onto the next one. Also, as each area has its own flavor, it means multiple authors can work on the setting without worrying about muddying up each other's visions.
Now take Cyradon, if I do not buy into the presented hook of refuges coming to the world, I am not really going to be buying any further suppliments, because it has established its tone and setup, and I either dig it or I do not. Now, that isn't to say Cyradon cannot be opened up to other areas, but the core book does not show that. I am not given a good overview of all these thematic areas to get my imagination working, to inspire me to run a campaign in Cyradon rather than build my own world from scratch.
Seriously flip through the Pathfinder campaign setting book at your local gamestore next time you are there, every two pages is its own entire campaign just jumping out at you, waiting to happen, complete with its unique hooks and background.
So I even if I choose to set my campaign in a portion of their world that has not yet been further developed, I am still buying into their campaign setting, and they have an entire line of products that are universal to the entire setting to entice me and my players. And I want to set my campaign in their world if I can, because they provide the groundwork details that I personally do not care to do myself: languages, calendar, holidays, dieties/religions, cosmology, major power groups/factions, races, and both global and local history.
I admit to not really knowing much about Shadow World, but it seems to be a very interesting world with some unique ideas. I fear though that it is too unique, and may not be appealing to enough people. Appealing to a large number of your customer base does not mean being generic, it means bringing a multitude of options to the table to pick from, so that everyone can find something they can use.
Is it easy putting something like this together? Heck no, I certainly could not do it, which is why I am willing to pay someone to do it for me.