The app also allows you to chat and play minigames with others in the stadium who are using the app. You can also order food from your seat with a credit card.
I guess it is b/c NoA's HQ is in Seattle, WA so maybe they sponsor the Mariners, that app is to be used to get stats and stuff while you watch the game. According to the description, there is even a kiosk where you can rent DSi systems so that you can follow the game on your system. It is like bringing a TV to the stadium with you so you can get those little behind the scene insights that the broadcasters give while announcing the game.
NOA headquarters is actually in Redmond not Seattle.