A game is a success if its a million seller over the lifetime of a system. FF will probably sell a buttload of games. Mario has and will continue to sell a buttload of games too.
anyways; I don't know how selling OVER 1 MILLION GAMES WITHIN ONE WEEK is a bad thing. I guess bad if you were expecting 2 MILLION GAMES WITHIN ONE WEEK; but if your only issue is that you only sold one million in a week instead of 2 million, then that's a pretty good problem to have.
I don't know why we're making such a big deal out of this. And then to say that sales will drop off? Well duh, if a game like SMG sold 1 million games a month, then it would be at like almost 6 million units sold by now (errrr whups... bad example). But of course there's going to be a dropoff. It would be absolutely insane to think that a game can continue at a pace of 1 million per month.
What would be an interesting study is 1st month sales vs. lifetime sales and the percentage of the lifetime sales comes from the 1st month.