Wii said:
Seriously why do Nintendo take money for games that already has earned their money? This is sick and I think they should be for free and everyone would buy Wii. Else they could make them a little bit cheaper than they already are.
From what I can see, you're paying for several things here:
1) The technology that enables you to play old games on your Wii. Nintendo did have to write emulation software so these games would play after all. It's exactly the same with GameCube titles, but people feel less annoyed at having to buy GC discs - perhaps it's because they have a physical product in their hands? Maybe it feels more "worth the money"?
2) Licensing/development/copyright of the games. They were programmed by somebody, why should those programmers not get paid for their work? Just because the games are old doesn't mean they have no value or are freeware/abandonware.
3) The service itself. Nintendo has created a special channel and arranged a back catalogue of titles. It might not seem like much, but this still costs them money.
When you think about how cheap these games are as well, it really isn't that bad a deal for a bit of nostalgia. Making them free also won't generate more Wii sales - having access to them is more likely to appeal to existing Wii owners who want a trip down memory lane.