This isn't really suprising to me when you think about how big Halo 2 was. Halo 2 grossed over $125 Million on the first day. *
Check out these opening day box office records:
http://www.boxofficemojo.com/alltime/days/?page=open&p=.htm
The highest opening day sales for a movie, EVER, was Spiderman 3, and that was 'only' $59 million. Heck, total gross for Spidy was $336 million and H2 did a full third of that on day one.
When you think about how much main stream hype and advertising latches on to a successful movie franchise, is it any wonder that similar things are happening with a video game that blows away any kind of numbers the entertainment industry is used to seeing?
*Source: http://news.com.com/Halo+2+clears+record+125+million+in+first+day/2100-1043_3-5447379.html