I've been watching a lot of pro Starcraft casts lately (hooray for Cholera!), and to me it's clear that skill is a major factor.
Using a build is just like using an opening in chess. It helps you make the first, say, ten moves. After that you're in uncharted territory. In fact, Starcraft players have it harder than chess players when it comes to the opening. If the player isn't timely with a scout into the enemy base, and then skillful with microing it, the player will have no idea what build the other player is using. Chess players can just see it on the board without any effort or probe/drone/scv micro skill. If you don't have that skill, you're not going to be able to adjust your strategy to account for the other players strategy.
A lot of the game also depends on your meaningful APM (actions per minute). Pro players have an APM around 250-400. The sheer concentration and quick thinking needed to maintain such a hectic rate of play isn't something that just anyone can step up and do. Using a good build has nothing to do with it. If you don't have good APM one or both of micro and macro will suffer.
Along with APM comes micro. In Z/Z, for example, a single well-placed plague can turn the game. For protoss, micro of a shuttle/reaver combo or of high templar storms can be crucial. I can't come up with a good example for Terrans, but basically in Starcraft your units are only as good as your micro.
Personally I'd take a skill-based game like CounterStrike or Starcraft over a level-based game like WoW any day.
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