they do, just not in yoko mode. most shmups in the arcade are in tate, meaning to get the actual effect of how you would play it in the arcade you have to rotate your TV 90 degrees so that it's standing on it's side. most shmups do have several ratio options as well as the ability to fully tate them. the screen just can't be appropriately displayed in yoko mode so they scale it down.
Its all good man...Thats how my computer room kind of looks like right now...Im working on getting a desk and all that together right now. Plus I need a display for all my action figures and walls scrolls