With an install base which was more than both new platforms combined.
Well FFX sold million or so more than FFXII with less than half the install base, baffling isn't it?
The install base argument doesn't always hold true, especially for first next-gen sequels on new platforms (GT3>GT4, MGS2>MGS3, FF7>FF8>FF9 etc). FF13 is the first one, guess it'll also be the highest selling one till the next-gen sequel.
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