The De Valk biography establishes quite clearly, based on lots of physical evidence, that no one did or even could have pushed Baker out of that window; rather, he fell from it all by himself. Also, De Valk provided James Gavin with all of this information and Gavin chose to perpetuate the pushed out the window story in his "Deep In A Dream" because it was more dramatic.
Yeah, the being pushed out the window theory sounds a lot better than just falling out of it; kind of like that pet gator in Russia