Why should people have to connect a pointing device to switch between modes that don't even require a pointing device? Sounds reasonable to me to have a way to do it... especially since it was doable before. It doesn't even have to be hotkeys... Tab/Arrows/Enter is the standard way to get around a GUI with a keyboard.
Well, When playing Taiko I get my wireless (hate me) keyboard, and sit comfortable and play it. But I'm too lazy to get the mouse / wireless mouse, so I'm using the keyboard to navigate through osu!... So ... why not?