I can see how this works in this particular case, with only Apple stores and while running a special app, but in the general case, how will they know that you're in their store and not the one next to them?
I don't know if Apple is using this here. I bet they're instead identifying it by store Wi-Fi, since Apple stores all have that already. But for stores without Wi-Fi, the sound system trick works well since all stores have sound systems already.
My current company is actually providing developers with a service (currently Android only) to provide better location contexts in their apps.
If you're interested you can take a look at our homepage from my profile. We just launched our public beta this week so if this sort of thing interests you as an app developer, please check it out :)