My assumption would be that Apple cycles their demo units into their refurb process. First, I'd expect the obvious time delay associated with that. Second, I'd assume demo units would not enter this phase unless a) they break, b) the product sku is being phased out in place of an upgrade. Besides, I don't think you'd find something labled "demo". I know I've never seen anything in an Apple store sold as an open box. I've seen a few at Best Buy, but I'm not sure if they are supposed. Similarly, I don't think you could count on any of those with regularity.