The games have broad appeal to audiences outside the normal "hardcore" audience. Hardcore fans are the ones who gobble up all the media and hype for games, and are raring to go on day 1, so these games sell huge in the first few weeks, and fall off the charts soon after. For the non-hardcore, they don't devote their lives to games, and expect the games to fit their lives, not the other way around; they will buy a game when it suits then, so a good game with broad appeal will keep selling as more people buy the consoles, and go back to the store looking for something else to play.
If a game can't get into this evergreen state, then its because it didn't have the broad appeal; either it's a hardcore game, or the game sucks and word of mouth kills of any potential residual sales.
WiiMusic? I haven't played it, but it doesn't sound very interesting.
GTA and Halo, they're hardcore, that's why they stopped selling months ago.
Veder Juda is hand crafted from EPIC FAIL, and is a 96% certified Looney; the other 4% is a work in progress.