Wii Sports had a lower opening week than GTA4, and now it's the best selling game of all time. Same with Wii Fit. It's reached an incredible level of sales despite a lower opening week. Gran Turismo 4 also came out during a time (winter season of 04-05) that saw the release of GTA: San Andreas, Halo 2, Metal Gear Solid 4, Fable, Half-Life 2, and a bunch of other games that I could go on and on with. Some games had smaller launches and longer legs if they were released around that time.