all it takes is a wobble. The disc is already spinning really fast, so even plugging in a USB cable could bump it enough to scratch the disc.
Granted, I think they should have made a better drive, as I've knocked over my Wii and not scratched the disc, most players have 0 protection from disc scratching if you bump them at all.
EDIT: unless it is scratching every disc you put in, it is your fault. (oh, and take spanky's post into account, so if you have a really loud sub or speakers near by, it would be your fault)








