Blizzard does not particualry appreciate petitions on the official forums. This does not stop players from starting them. Lyccan of Ner'zhul started a petition in the Suggestion forum to make the Recruit-a-Friend benefits retroactive. At this time Blizzard has announce no current plans to give these rewards to folks who have brought players into the game in the past.
Most of us are pretty open about our love or World of Warcraft, and many of us have invited our friends and family to join us in WoW. In the past, the joy of sharing the game and a potential game-time buddy was enough to bring our friends into the game.