Problem one: A mouse still offers more granularity than your finger
Problem two: Starcraft is not the best "quick game for a fun little diversion". Maybe I've got the wrong idea here, but IMO RTS is the Monopoly of video games, and I don't play Monopoly on the bus.
I can definitely see playing a quick starcraft game on my tablet as a fun little diversion while I'm on public transit or something.