I'd say strategy is giving the player choices to do an assignment. You might have only a few such as sniping from far away, or stealthy approaching them in a FPS like 007. In SC, you have nearly 100 ways to approach a situation thanks to a beefed move list. What seperates strategy from just moves is what each move does differently.
In SC2's case, some moves attack vertically, others do it fast or slowly. You have to consider which move is the best for the situation. Finally, a strategy game has to have nearly the same amount of equipment for each side, such as black and white pieces same in number, in order for the game to be based on tactics. In RPGs, a level 40 Mage is obviously going to beat a level 3 Warrior, despite his counter. Strategy is not about statistics. Statistics predict who will win.
Strategy is about making the decisions more than anything. Other games, like CS, that I have mentioned, have the player focusing on perfecting one skill such as aiming in shooters, driving in racers, or jumping in Mario, to be a strategy game. Strategy games aren't about how you do something, but whether you actually do it or not.
The way Bobby Fisher moves a pawn is the same way I move a pawn. That's my point. It's about choosing the right thing to do, from a pool of choices, rather than perfecting a skill like aiming.