Supported - it works Not supported - it'll probably work, just don't expect any help off us if it doesn't. So when they say linux isn't supported it means they won't provide drivers and/or can't [won't] help you if the open-source drivers or *insert motherboard feature here* don't work under linux
So in other words if you depend on us to fix a software problem with the hardware you bought from us we won't help, i thought there were two people in this world, people who call tech support and people who make fun of people who call tech support.