OK one more time: this clip does not proof anything, as it only shows VERY FEW units on campaign map. If you find a video which shoes 200-400 units on a multiplayer map while in a fight, we'd be talking, but this video is totally useless if you want to rate the MBA's ability to PLAY SC2...
Well, before this question, I didn't see one answer on this, so I'd hardly think it was a one-more-time, issue. But at least I could compare apples to apples when it comes to comparing it's performance on that same scene compared to what my machine did, on the same scene. Though to be fair, SC2 is still a very good-looking game and doesn't spare expense in terms of unit and building animations even at the low settings. However, as you say, the true test is in multiplayer, for which I can still run the low settings while a major raid is going on, and tons of units are in play. Even in the midst of battles there's not even a stutter. Though on my late 2009 MBP 13" model, you may see a slight frame pause if you decide to bump the textures to the medium setting. If kept to low, large scale combat seems rock steady on OSX. Very nice of Blizzard to support smooth gameplay on a 9400M, even when the screen is just plain filled with units.
People will ask these questions, just because they wonder if their non-gaming machine can still run their favorites. Others maybe aren't really shooting for the moon, but if they know it would run X, they know it could run everything they really wanted that is less resource heavy than X. Others are just curious what the "tiny machine that could" could do.
Though to be fair, this isn't MacBook air specific. If I had a nickel for every person that bought a cheap windows laptop, with the intel integrated graphics chip, and got interest in gaming on one of those, I'd be sitting on a beach owning 20%. At least this topic is nowhere near the same level of tall order.
Still, hopefully some more answers will come, just for the fun of it. Heating issues may be a factor here. Perhaps unlike my MBP, even if the Air proves it's graphical might, they might only be able to pull this stuff off in short sessions; whereas I can push my MBP for hours and hours and it'll still perform since it seems to keep things reasonable temp.
If I were to get the Air, it would mainly be for what seems to be the best desktop experience for an ultra-portable.