I also love the idea of challenging people to think big, like what they'd do if they ran the world. For me, this question involves ethical considerations, prevention of global conflict, the battle of hunger and poverty and the maximization of happiness.
I don't understand how their microactions relate to that question at all. They seem to be asking two questions at the same time. One is a hypothetical mindgame that makes people think about the challenges of the world and one is the very specific question of what each individual can do. As a result the answers they get are apparently either overly general or not relevant at all.
If anyone wants to discuss the big question, you can check out a thread I recently opened at HN :)