Well actually Starcraft has the most difficult Micro because unlike WC3 where units have huge hit points, SC has units with no more than 150 hit points.
If your referring to massing of units you must mean games using money maps or UMS like BGH and fastest maps. Real Pro Gaming maps in SC are very hard to play skillwise and hardly last more than 15 minutes on average per game.
Starcraft is a game for real competition, not for fun or bragging rights. No wonder its still the most played RTS in the world. Right now it is not only Korea that has pro gaming teams for SC but Europe is starting to form its own teams.
Not bad for a game that has been around for almost 10 years.
