Having worked a store, I can understand the frustration. But it's usually because Nintendo only sends us ten each shipment--and that's on a good day. During the holiday season, that lasts about fifteen minutes.
The employees get upset because they're losing business that's all but garuanteed. The customers get upset because the store doesn't have what they came in for.
Nintendo doesn't let stores 'order' product. They send us what they want, when they want to, and at the quantity they see fit.