According to wikipedia, Capcom announced in 2007 that RE4 had sold 1.6M for the GCN and 2M for the PS2 worldwide. Whether that's true or not, it's well known the game sold well on both the GCN and the PS2. It was certainly an advantage for the GCN at the time that it released about nine months earlier on it, but it's definitely a multiplat in terms of its sales split.
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Praise the Black Turtle, Game of the Decade Guru Champ.
(Well, I never promised creativity, did I?!)