Re: The reason Microsoft decided not to allow PC gamers to take on Xbox gamers?
Doesn't take a genius to figure that out. I mean you're comparing moving your thumb with fine movements versus moving your entire hand. Also, with mouse and keyboard you can hit multiple keys easily (e.g. two directions, fire and jump at same time, etc.). You can hit multiple commands on a controller, too, but it's awkward.
Mouse and keyboard just offer a better range of controls. Only games where controllers would have an advantage (or be on par with mouse and keyboard at least, imo) would be sports and racing games.