It doesn't mater what it could do as long as it was useful and cool looking. What better way to show off the sdk power than to give us a new app? Wet out appetites so to speak. Imagine if during the keynote, he said everyone turn on your iphone(probably 90% of the people there had one, and those not what better way to make them feel bad lol) and call send a text to this #. A minute later everyone's phone is sent a new app and they follow along as he demo's its power.