why don think the marketing won't be there?
and do you only think about the opening,sony has never been good at it
there will be 5 of the biggest shopping weeks following the unofficial gt5 release date,even if they start during them.the sales will be massive as people will be buying then and a great product will sell in big quantities
and do you know how games sales slide after launch
if GT5 launches at 500k then expect it to maintain the same sales or bigger for every 5 weeks till the end of the year