Do keep in mind that you can always use the game codes ('nba' and 'nhl') as aliases for the current game ID, at least when requesting base level game data (I think there's a bug that's keeping that from working in all cases when you try to filter collections to certain keys)! So if you requested something like:
CODE
http://fantasysports.yahooapis.com/fantasy/v2/game/nba
It would give you data for whatever we think is the current game ID (and tell you that game ID in the response). ...I'm actually not even sure that I want it returning back game data for the current season before the game has launched, but there it is. :P