Yes, Halo Wars will sell more in the first two months. The biggest factor for this will be the amount of hardcore Halo fans there are in the US, and the amount of xboxs there are in the US, compared to all the playstation 3's in Europe and us European's tendecy to sit on our asses and not buy ace games for a month or two after they come out.
Halo Wars first week sales might be double the Killzone 2 first week sales.