Maybe the PS3 and XBox 360 are losing in Japan out due to their form factor and controller?
The Wii is very small and the remote is innovative. It's a fun console and those predicting a demise due to the novelty factor wearing off are missing the sales volumes. You simply won't see a console dying off when it has a massive user base.
I don't need amazing graphics to have fun, just like I don't need tons of special FX in a film to enjoy it. Films need a good plot and story, computer games need good gameplay and fun!
Too many console games try to simulate football and driving games as realistically as possible, but why? it will never be realistic until you feel G-force and feel the wind blowing past you.
Many Wii games on the other hand don't try to be realistic, they try to be fun. Mario Strikers Charged Soccer is a fun football style game (it's like a blend of Speedball 2 and Football) and totally unrealistic. So is Excite Truck, 4x4s flying 30ft in the air and driving at impossible speeds, but it is a lot of fun.