Linux Mint is not copyrighted.
How is this anything but patently false?
Any part of Linux Mint which came from Ubuntu (which as I understand is the vast majority of it) most certainly IS copyrighted, under the GPL or other FOSS licenses.
Also from your About page:
You can use it, modify it, distribute it and do whatever you want with it. This is our idea of freedom and we hope you'll enjoy it.
No, you can't do whatever you want. You can't violate the copyright license that any code in Linux Mint is distributed under.
I get the idea that the Linux Mint project is not as idealistically free-software minded as Ubuntu, and that's fine. But I think the claims on this About page are at least misleading, if not totally wrong. I hope you consider rewording it.