I'm still not sure I understand what made that so heretical other than being different. I can't really imagine any scenario where I'd be using the start menu and want to see something else at the same time.
The reason why you need to open the start menu is often on screen, then you hit the Windows key and the context that should be driving your next action is hidden. All it takes is a brief moment of distraction and — if you're like me — you'll completely forget why you opened the menu in the first place.
It's like walking into a room and forgetting why you had entered. At that point, maybe you return where you came from and see an unopened package. Then you remember: you were retrieving scissors.
When the motivating context is in front of you, it's easier to remember what your goal is.
What I thought was nice about it was that, if you're primarily a search user, you got a lot more real estate for the search results. I suppose they achieved some of that in the new design and the feedback has been pretty close to unanimous, though.
