As a nattering naybob of negativity, I must point out that this falls in line with what has been done with the core rulebook -- instead of one thick $40 book, you get two slim $25 books.
I will say this might actually be a good thing if done right -- by which I mean a player cult book, and a GM enemy cult book.
I've been out of the retail business for a long time, but I seem to remember that shelf-space was precious, and I wonder how the multi-book strategy fits into that...