Repairing DVDs?

[crazychicken]

I have one of those memorex "cd repair" kits that has the buffing wheel that spins around and rubs against the disk for a minute or so. I guess the idea is that with CD-Rs the data is on the label side with plastic between where the laser lives and the data itself. However, aren't real cds and dvds "pressed" - meaning that the data is on the side where the laser lives? If so, aren't you basically erasing the data by using one of these things on a dvd that you buy from the store?

Maybe I am missing something (maybe=probably haha).

Hopefully someone can steer my understanding back to the track.

Thanks,

Dave