The "Wii would like to play" campaign was chosen because it expanded demand for the console by avoiding the obvious strategy of targeting the teenage male gamer and instead focusing on his mum, dad and grandmother.
The Grand Effie decision was based on a deliberation of the top five scoring Effie campaigns by a jury of top marketing executives from the client and agency side, led by Deborah Meyer, vice-president and chief marketing officer at Chrysler.
Along with Leo Burnett the other four Grand Effie finalists were Anomaly Communications for the Keep a Child Alive campaign "KCA's media ambush of the iPhone launch", BBDO New York's campaign for GE's "Ecoimagination Round 2", JWT for Kimberley-Clark's Kleenex "Let it out" campaign, and Secret Weapon Marketing for the Jack in the Box "Sirloin vs. Angus" campaign.
Meyer said: "Leo Burnett's marketing strategy for the Wii will forever change the gaming industry and its dialogue with consumers."
WPP Group won the most Effie awards with 26 agency wins, while Omnicom agencies had 21 wins.
Publicis agencies were awarded 15 Effies, IPG landed 11 and Havas took home six awards.
San Francisco-based Goodby Silverstein won the most Gold Effies of any agency in the competition, taking home three Gold trophies for its campaigns for Adobe, Doritos and HP.
Mary Lee Keane, executive director of the Effie Awards, said: "The most memorable Effie winners from the last 40 years were also the most creative and innovative, proving that playing it safe isn't always the most effective approach."