It's an indie game. Huge phenomenon. (actually.... "What's Minecraft" makes me want to ask if you've been under a rock for the past year.
)
But not so huge that it would have any bearing on major game sales.
And anyway... most Minecraft users right now (it's technically in "Beta", but...) have already paid for it. It was $10 during Alpha, for lifetime updates.
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Edit: Some words about http://tvtropes.org/pmwiki/pmwiki.php/Main/Minecraft