As I already said blizzard include 3 options. Fullscreen, windowed fullscreen and normal windowed. Fullscreen makes the other screens go blank, windowed fullscreen gives you fullscreen while the other screens dont go blank and windowed makes it windowed.
There is one really important reason fullscreen makes the other windows go blank. As an example I will use starcraft 2 and normal fps games.
If your other screens dont go blank this means you can move your cursor into them. When you do this in starcraft your map moves to that direction. And you have to move the mouse much further to get it back on the right screen. This lost me 10-15 games of sc2 before I decided I had to play with proper fullscreen. God forbid you click on an application while you are out of your screen then you loose even more time. The same things go for FPS.
Going fullscreen windowed mode gives you full functionality on your other screens, it gives you fullscreen on the game, and all graphics and stuff work as in fullscreen.
So what is it that he lacks in these options? What he says he want is all in the function windowed fullscreen.
If you disagree I would really like to know what functions that work differently.