i've read about it on other message boards... these things are already in stores, and it's not just gamestop doing it... here's the deal, as reported by others...
starting on the 10th, nintendo reps were visiting stores and changing out the demo kiosks. stores with only one unit (best buy, walmart, etc.) got their nintendogs demo replaced by the new metroid pinball demo, as we've been seeing. stores with 2 units linked together (gamestop, ebgames, etc.) got advance wars replaced by metroid pinball, and nintendogs replaced with an updated nintendogs demo, which includes this haylie download. so this gift is actually available at other stores.
this event is just a special nintendo/gamestop/spca thing. a certain percentage of nintendo sales are going to the spca over this weekend. the download is just a way to help advertise the event and get people in the door.