The strategy of not putting everything that should be in a core book actually goes back to 2E.
So, for monsters you bough this binder. That had like 12 monsters it or something, and you basically had to go out and by other monsters packs to get anything. They where doing the fighter book and I think the magic book (or at least planning them) even as the PHB was comming out. And the DMG, the DMG had like 1/3rd of the content of the 1E one, and these brown supplements to cover that followed very shortly.
3E nominally tried to step back from this strategy. But they didn't quite get there, and underpriced the PHB. So they did a reboot...new corebooks and tons of splat.
And then there is 4E....
Actually, each of the last 3 editions has done a redo on the MM. So, I am really liking the more expensive and expansive approach, with a focus of getting it right the first time. There is every indication that each of these books will have a lot, more then enough for most campaigns for a long time. And the plan is to support on the adventure/campaign side. Not with a wall of splat.
I am feeling a little more excited.