And even then, every tweak made by a motherboard manufacturer has to be taken account of. It's like saying the AMD "supports" running Linux on it. Course it does, but it doesn't mean that the computer can actually run Linux usefully (Argh! Flashback to the days when a lot machines *couldn't* get basic support under Linux working without patching an tweaking).
It is much easier when you have support from the manufacturer. Previously, AMD would provide preriodic code drops and makes their engineers available. Now, one of their more recent contributions provided the same code that BIOS manufacturers get.