They did put 'keyboard/mouse on the one poster (not the tree), but I think the PC gamepads wouldn't be good inclusions because they are always direct copies, rather than derivative evolutions. I've personally only owned three PC game pads in my life: My Gravis GamePad looked exactly like a SNES game pad, my WingMan was just a N64 controller, and my current gamepad, the Saitek p2900, is just an XBox controller.

Notice that the chart also didn't include any console controllers that didn't make any improvements on the previous generation (for example, the NES controller that came with the 'new' NES was literally just a small SNES controller with fewer buttons, so it's not on the tree).