It wasn't 1m units in 45 days unless they sold over 900k units in four weeks. First month sales were 86,633. Assuming this is for the month of November with a Nov. 13th debut and about two weeks worth of sales.
http://www.next-gen.biz/index.php?option=com_content&task=view&id=8352&Itemid=2
http://www.joystiq.com/2007/12/14/crysis-sales-in-crisis-ut3-gets-fragged-too/