I also prefer the new approach where they offer a series of different stories which are often mutually exclusive, and are clearly labelled as suggestions. It keeps things looser and stops meta-gaming players knowing every detail of their environment.
I actually support the 'reprinting' of various 40k rules in various books, as these aren't supposed to be a completely compatible rules system, and the format allows crusty long-term fans to simply pick up the version that appeals without need to invest further. I've bought a couple of systems now, but originally only intended to buy one, and would have been aggravated at the thought of shelling out for two hard-back tomes; especially as I originally intended the book to be more of a bookshelf piece than something that I actually played heavily.
Plus they get to hone their system and make improvements and fixes: Something that could not be done so easily with a core book. The shame of it is that FFG have fluffed it slightly and not made all the changes that were needed to hone the core elements and further dropped the ball with some poor errors due to cutting and pasting old rules and passages.
I don't agree that it's taken 4 editions for WW to get it right if you are referring to inter-compatibility of systems, though. The mechanics are shared, but the systems really don't work together well, and I don't think they are really intended to be used in some mega-game. I certainly don't know of anyone who runs or plays a game with 'varied' PC types, and I don't really expect FFG to loose much sleep trying to reach the point of perfect compatibility which has eluded WW for 20 years.