I watched a pro game just the other day where one of the players noticed that their protoss opponent had a late timing on their second pylon in their main base - as in, it should have been there, but wasn't. That protoss player has a well-known penchant for early game stargate harassment, so the other player read this situation and reacted by delaying their first expansion and instead producing early-game air defenses.
As another example, take unit composition. If a terran player is running a bio-based army (marine, marauder, medivac), what sort of units should zerg produce? Infestors are usually a good choice in this matchup. On the other hand, mass infestors will be much worse against a primarily mech-based terran army; instead you might see many vipers on the field (which, vice versa, wouldn't be great against a bio army).
Pro players are essentially always scouting what their opponent's doing because the macro decisions can make or break the game. The general sentiment I've seen that is good macro skills will push you far up into SC2 leagues, and it's not until diamond/masters that micro starts to really matter.
I watch a fair bit of pro play, and also play enough to bounce between low diamond and high platinum on NA. It is almost always my macro that wins or looses games.
Most people at my level wouldn't even have consistent enough play to be able to notice the difference between well and poorly micro'd games. But if they miss an upgrade, or build the wrong comp, or worse, don't expand, that is the win/loose for 98% of games below masters.
Which all around sucks for me, because my micro is on point :)
Some good but not quite star quality players like Ketroc deliberately ignore the meta. Ketroc plays with loads of Ravens, he did this when people said Ravens were strong but hard to use, he still did it when the accepted wisdom was that they were now useless, and last time I looked he was still at it after yet further balance changes to SC2. How he uses them changes, but he likes Ravens and they never stopped being viable.
Games like Chess have meta too. A year ago humans believed that materiel was essential and strong position made up only for small differences like losing a pawn or two. Then Google's Alpha Zero AI says hold my beer, sacrificing loads of my pieces for positional advantage is fine, because I can use that advantage to pin your extra pieces and still mate you away.
I think that SC2 and BW differ in this respect because SC2 has been constantly updated throughout its competitions to make more strategies and units viable. The last balance patch for BW was two years after release in 2001 (although a recent bug fix is said to have slightly buffed valkryies, there is some dispute about whether this actually pans out in practice but I haven't looked into it).
Thus, strategy is the widest tent, and someone like sOs shows the truly massive number of strategies that can be employed. In contrast, macromanagement does indeed have a smaller decision space, since really the "decision" with macro is pre-defined. Make your economy and production as efficient as possible. There may be slight variations in how its done, especially in Brood War where the economics are much more nuanced than SC2. Nevertheless, if you watch a variety of pros macro out mass marine-marauder-medivac, they will usually have very very similar expansion timings, identical numbers of barracks, and any changes in the timings/build orders is strategic, not macro-related. There may be "on the fly" macro adjustments due to harassment damage, however strategy is far far more fluid of a category than macro.
When it comes to micro and decision space, however, I believe that it is mostly a matter of execution and not decision. We've seen perfect blink micro stalkers, dragoon AI bots, and I think it'd be far easier to take down top players in a 1v1 micro fight since computers are not limited by mouse accuracy, emotional concerns, stress, fatigue, and a number of other factors which affect your hands' abilities. In contrast, a top player should have a much better edge over a computer in strategic realms, since strategies must be tailored to the expected opponent's strategy and mind games heavily factor into this equation.
God, what a beautiful game.
The basics (Spend your money, don't queue units, don't get supply blocked) are trivial. Executing them perfectly for 20 minutes, during a stressful game, is impossible. The best players in the world can't do it.
If you ignore the part where you have lots of choice, then there's little choice, indeed :)