Welcome to being part of the minority for once.
I can understand that some gamers will really never understand the Wii. People who have spend the last ten years diving into deep complex games, playing hours at a time won't understand that for most people, with busy lives and many hobbies, gaming is mostly about social interaction and just having fun for short bursts. If your idea of fun is learning an ultra complex button combination and perfecting it over a few hundred goes, then the Wii just may not be your cup of tea.
But i can probably tell you why the Wii is selling so much. The main reason is because for decades, whilst gamers were out playing GTA, Halo, WOW etc., most gamers, including just about 80% of female gamers, were on yahoo games playing Diamonds, doing crossword puzzles, or playing board games when social interaction was the main goal. Nintendo recognized this and brought out the DS, pretty much a handheld version of Yahoo games.
I think what hardcore gamers never realised, is that they were always in the minority in terms of numbers. Yes 120 million people bought a PS2, but hundreds of millions women and girls were playing games on the PC. Yes in the states over 90% of women play computer games. And honestly, how exactly are the 360 and the PS3 catering to this demographic? I don't see cheerleaders getting excited over multiplayer Halo, or moms bugging their kids for one more game of Grand Turismo. But when people are gathered together, of different age groups and demographics, lets be honest, who does not want to play Wii bowling with grandma, if only just to a 93 year old woman enjoy gaming?