Going by history, some people on the COMGnet thread pointed out that preorders for the MH series are a larger percentage of sales than the preorder numbers for pokemon games. So basically, historically at least, if a pokemon game and a MH game both had the same preorder numbers at launch, pokemon would open higher, because it's overall numbers are less represented in preorders. More people go in and buy without preorders.
Of course, MH appears to be growing in popualrity, so maybe things will change.








