You're comparing apples to oranges.
StarCraft 2: Wings of Liberty sold 6 million, but only small fraction of the playerbase is interested in competitve aspect.
Minecraft is just an online sandbox. Most people will play it like that.
Plus a gamedev doesn't need to take into account what sells, but what kind of competition you have. How will your Minecraft clone exist in market with Minecraft vs how will your M
RTS live in a market with StarCraft 2.