It can be tough to notice I admit. Especially in something like a menu.
I actually use the Wii on a 16:10 computer monitor that has component inputs, and I honestly don't notice a difference of using a slightly different aspect ratio (Sadly, since the signal is 4:3 from the Wii that the monitor has to then stretch to fill the screen, there's no way to get a 16:9 AR out of it on my 16:10 monitor).