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.
The rules have changed. Now that new recruits are rewarded with a fancy new mount and some snazzy bonus experience, many who have brought friends into the game want those rewards as well. Calliope of Ysera echoed the sentiments of many with, "I think this reward system should go for all players who recruited in the past as well. This is like a slap in the face to those who already brought Blizz customers."
Blizzard doesn't see a need to make these rewards retroactive. This is a move to entice new players. Theoretically it will also keep existing players happy if they manage to recruit new players into the game. There is very little point in being bitter, many things have changed in WoW, like decreases in mount prices, that the developers have not seen fit to make retroactive.
Is WoW's popularity waning enough to warrant Blizzard turning it into a gamer's pyramid scheme? I have a friend who's been itching to give WoW a try, with the new incentives, I may just buy him a copy.