I would strongly encourage you to go against your preconceived idea of what StarCraft is (a game where people compete on who's the fastest to bash their keys) and see a professional game and all the strategy it entails, such as in the semi-finals and grand final that will be on today. Pro players do have valid reasons for having such a high APM (even if a portion of it, maybe 30%, is just "spamming" to keep theirselves active and ready), but you can be an excellent player with rather low APM (~120 maybe?). Why would you need to do 2 action per second? A lot of it is simply building units periodically (e.g pressing 1 then "S" every 10 seconds) but then APM really gets high when there is a battle and you need to give actions to multiple sets of units to get a good engagement.