I think it went something like this:
Shuhei Yoshida and Co. walk into Activision's offices and be like:
"20 Million consoles sold BITCHES!"
And Activision guys be like:
"Give that men some exclusive COD content."
Nintendo is selling their IPs to Microsoft and this is true because:
http://gamrconnect.vgchartz.com/thread.php?id=221391&page=1