I generally agree, most of Nintendo's titles are built on gameplay, which contributes to great replayability and their high sales. Games with this sort of focus are generally the best sellers for any console, really.

The HD consoles are no exception, Halo / CoD / Gears have robbed all the top spots, thanks to the introduction of online multiplayer. It's the lasting gameplay that sells these games.

And why exactly is the Wii market so different? The extremes of both consoles are different, but there is significant overlap. The "regular" gamers are the bulk across the board.

I dont agree that there is a "SIGNIFICANT" overlap. there is but its not on the level the the companies are focusing their advertisements or products on the same age group. wii consoles were geared to casual gamers. check link: http://www.businessinsider.com/wiis-secret-to-success-young-boys-and-old-women-2009-2  hence the different market. people make hard choices between xbox or ps3. not xbox or wii and ps3 or wii. usually people have xbox and the wii or ps3 and the wii.

wii offers a different experience compared to the ps3 or xbox.

Back in the day, videogames were things you did replay. Nintendo goes OLD school in its designs and they do things that do have replayability and you keep. Oh, there are some exceptions, but on the whole they are replayable.  The arcades did compel the videogame industry to make games people would keep pumping quarters in to play.  Nintendo has origins in the arcades.

Contrast that with games as movies mentality videogame industry has now, where it is supposed to be an awesome play through once experience. When you create replayability, games don't end up in the used bin, so thus you sell more.

I hate the game as movie mentality! Games to me are games they aren't movies and they will never be movies no matter how much people try to shoehorn them into being movies. I like games which are as good on the fourth playthrough as they are on the first. I don't even count a game as amongst my best ever until I have sunk over 100 hours into them. If a game cannot last me 100 hours then its not fit to be called great.

Nintendo games are more fun to play than others and when you finish playing the game the first time, you get that feeling to play the game again.