Dunno why it hasn't been implemented yet. Any guesses?
EDIT: For offline friends.
Isnt there a button that you can click on there to chose between "sort by name" and "sort by status"?
Yes, of all the things Riot has on their plate, this should definately be put on the top of the list.
© 2013 Riot Games, Inc. All rights reserved. Riot Games, League of Legends and PvP.net are trademarks, services marks, or registered trademarks of Riot Games, Inc.