Cracks and scratches on unibody macbook

I have a new (3 month) old unibody plastic macbook. It has always been housed in an incase custom case. Never dropped. Always used on my lap. It has developed scratches all over the lid - only the lid. The lid has small hairline cracks coming from either side.
Taking it to the apple store, I was told that I must have abused the laptop. Also that the cracks come from opening up the lid all the way against the stop.
I guess my question would be, has anyone else reported similar scratching or cracking. This seems somewhat extreme that I would see this after so short a time.