I read something awhile back where it stated that scratches dont do damage as long as they dont penetrate the outer protective layer. So what you said is true the scratch has to be deep to do damage, so its not the size that counts but rather the depth.

it's not exactly like that: deep scratch can cause the laser to not reach the data layer for irregular reflection.. so If a single file is corrupted that way (deep scratch in the rotating sense of the disk that cover an entire data block) the disk can't work.. however fine scratches reduce only the reflectivity and laser can increase power to read properly the data..

Late reply but maybe your just touching the sides of the Wii putting it in. The Foam on the sides of the slot are there to put your disc in safe and clean the disc while going in. maybe when the game is in your Case it's moving slighty. Don;t worry about it until it effects your gaming

I don't think it's the case since the scratches are very straight.. probably it's just some grain of dust that is on the foam.. if you think about it.. the foam retains the dust on the disk.. this way it preserv the system from dust.. but the dust grain can demage even very softly the disk.. it's normal I belive

You may have to change your Wii. I wouldnt trust it. My WiiSports is scratched because of that cheap ass paper case and Zelda is clean.

This may be off the topic. Every time I put in a new Playstation game and play it for a while, it gets these smudges like the material is eroding. the GCN and wii are clean as a whistle.

I can see some sort of smudges on the wii disks too on the outer zone, but that may be some industrial remanent, like for ps2 games (I live in europe so games may be produced in different way).. these are not scratches because the more I use the game the less I see those traces..

The scratches I'm talking about can't be seen in normal light.. the only way to find them is to use a strong light at a distance of 20 cm from the disk.. this way (looking very carefully and turning around the disk under the light) I can see those scratches.. under normal light no scratch can be seen