This was written 4 days ago and says Bioshock Infinite sold 4.3 million units, yet the Wikipedia page says it has sold 11 million copies. Where is the disconnec

This was written 4 days ago and says Bioshock Infinite sold 4.3 million units, yet the Wikipedia page says it has sold 11 million copies. Where is the disconnect? Seems like a huge discrepancy. Is "units" normalized to full price or something where "copies" just total games sold even at sale price? That is the only guess I could come up with.