Users reported this since 2007 (https://discussions.apple.com/thread/1167366?threadID=1167366&tstart=0). I have a 2010 iMac and it's the same. Maybe all subsecuent models scratched disks until they dissapeared the DVD slot on late 2012 iMacs. They hided that little problem from us when we bought it.
As some user posted somewhere: "The slot is too narrow and to sharp". That's all about it. It was defective by design and that's why Apple couldn't do anything but offer us to buy them an external unit.
I guess It could even cut a carrot or produce a severe injury on a kid if he rub his finger inside the slot.
If you are EXTREMELY careful you can manage to insert a disc without scratching it. Just avoid the disc to touch the right wall because it's sharp as a knife. I close one eye to have more precission, use that tip if you want.
I'm still angry with Apple but I'm right because scratching disks is not what you expect from such expensive computer. More than that: I'm pretty sure that the cheapest computer in the world doesn't scratch the disks.
Sorry for the rant. It's just that one day I was very excited because I was going to watch a very old and irepleacable family movie on that gorgeous screen and the iMac destroyed it.
