It's reprehensible that they aren't directly funneling all profits to the creator of the Box2D framework. All they did was skin a few Box2D function calls.
I suppose if that's "all they did" - any of us who could do that could've been sitting on that 3 billion, right? Heck, even the Box2D guys could've done it.
There's a small difference in saying "they should've employed the Box2D guys" or "generously funded the project" and "they should funnel all profits" - perhaps Rovio deserves some credit here for turning a little casual iPhone game into a household name.
Why was Crush The Castle not as successful? Marketing and polish. If your aim is commercial success, it's obvious what your focus has to be.