I think the game will have staying power too. So far, it's been the multiplayer GCN games that have had it while the 1P games have had very short stays on the charts.
I think the connectivity feature will also help. The people who have bought the game will be inviting their friends (who ALL have GBAs, because it's Japan) over to play which will get them interested in the game.
Basically, this game and the connectivity feature have both had big question marks over them. I think most people in Japan have been doubting whether this spinoff FF title was going to be anything special and if the connectivity was going to be all Nintendo has been making it out to be. Now that the game is released and presumably getting good word-of-mouth, hopefully people's doubts about the game will be removed and they'll be rushing out to buy the next shipment.