My Wii story is, I'm sure, fairly similar to others and IMHO the reason why the Wii is so successful.
Consoles owned in the past PS1 + PS2.
Had lots of games for both, used to play them both lots, mostly on my own.
Started getting bored of PS2, only games I ever played were dance mats when we had people round, or Tiger Woods when my friend used to come over. Never played it on my own and my girlfriend found it boring, so it went in a box upstairs, not seeing the light of day very often.
Next gen was talked about, I had no interest really, despite being a techy and working in IT.
Then read a news article about the Wii before it was launched. Thought it sounded very interesting and a very good idea. Kept looking for updates on it and it looked more and more interesting. By the time it was launched I "needed" one. Managed to convince myself out of it for a good few months though, thought it would end up the same was as my PS2.
But then got one and my only regret was that I'd put it off for so long.
I now play it most nights. My girlfriend plays it with me, either against me on Wii Sports, or as a 2nd player co-op on SMG or just taking it in turns with Paper Mario.
Whenever we have friends over, the Wii comes out, either Wii sports or Mario Party 8.
My dad (59), who never showed any interest in computer games with my ps1+2, occasionally comes over for meals and stuff, always wants a go at the Wii. Loves the Tennis. I invited my parents and my girlfriends parents over for a BBQ earlier in the year. Both dads played the Wii for a couple of hours. Gf's dad now wants one (and is getting one for his 48th b/day next month)
Over Xmas wherever I went I took the Wii. It was always played by everyone in the house, regardless of age and everyone seemed to enjoy it.
The Wii appeals to a lot more than the small % of gamers. It seems as simple as that. People who would never even think about playing a games console are seriously considering getting one. The Wii's simple user interface and Wii Sports, with it no (or very few) buttons to press, seems to be the reason for this.
It's also reinvigorated my love for games, as it's fun, which IMHO are what games are supposed to be