You simply can't combine the competition, here.
Sony looks at them and thinks "We want to beat Nintendo" and "We want to beat Microsoft." Not "We want to beat Nintendo and Microsoft combined by X amount," because it doesn't matter to Sony what Microsoft and Nintendo make COMBINED, since each company only sees their portion of the sales. When people compare Sony and Microsoft, they don't go "Oh, and add Nintendo's numbers to Microsoft's." They compare them straight up.
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SEP Nash, Smelling Like the Vault since 1996
Step FOUR! Get Paid! http://i33.tinypic.com/2v1sq51.jpg