Hmm, I always thought that this style of teaching was a good way to lose a lot of students' interest. A math professor I had was insistent on showing the thinking that led to a proof, which not only made it easier to remember, but also made the study vastly more interesting and engaging. From what I can gather, his technique has made him quite a popular professor amongst the students at the University of Waterloo, so I suspect this is quite an effective alternate style of "intro" course, although I recognize that it limits the breadth of material.