Provided the cross-references aren't so extensive as to swamp the book, this sounds like a good thing.I think the major effect this has in practice is that you will see supplemental material refering to other supplemental material. So,Arcane Power will have supplemental material (powers, feats, paragon pathes, variant class abilities) for the Swordmage, even though the Swordmage was only in a Forgotten Realms specific book.
I also like this. I didn't get the FRPG because I have any interest in the Forgotten Realms. I just wanted rules material.Certainly there is a certain change in the way the campaign books work in that most or even all of the material is designed to be usable in different campaigns. So even someone playing only Eberron or a Homebrew campaign will find rules stuff in the Players Guide to Forgotten Realm or Dark Sun that he find useful (and compatible).
What I'm trying to work out is what is meant by saying that WoTC have taken this route, given that the books I mentioned are labelled "Supplement" and not "Core".It seems WotC is taking the route to say "everything is core" as there is no more optional material
OK.It's referring to the fact that everyyear there will be a new PHB and DMG and MM. The others are, as you say, "officially" supplements.
Were the PHB2 and DMG2 labelled "core" or "supplement" in 3E? I've never looked at them.
I think the MM2 was regarded as core in 1st ed AD&D. Certainly we treated it that way when it came out.
I'm still not really feeling the force of the issue.