(2) This is the 21st century. Consider that most computers do not have a keyboard or a mouse. Try designing a UI so it can be useful with or without a keyboard and with or without a multi-button mouse (eg. only a touchscreen, or maybe somatic feedback while using your Holograph goggles).
I'm not sure that all games benefit from this: I feel that some games are well-suited to touch-screen controls, others are well-suited to mouse-and-keyboard, and yet others are better-suited to other input mechanisms. Attempting to force one's UI to be suited to a touch-screen may result in a poor interface on non-touch-screen devices, or simplification of gameplay in order to reduce the number of inputs.
That said, if your game is suited to touch-screen input, or you have sufficient resources available to allocate to investigating an alternative touch-screen UI, then I believe that I do agree: after all--and all other things being equal--the more platforms a game is available on, the better, it seems to me.