This is foolish nonsense. I have installed AMD AHCI drivers on countless computers (Albeit 32-bit WinXP) and I HAD to have the drivers available because Windows XP installation won't see them without the textmode drivers on a floppy or slipstreamed on the CD (If you slipstream it, you also have to slipstream the regular drivers and not just textmode or you will get a BSOD after installation).
The drivers are readily and openly available on AMD's website:
The dates are October 10 2010 for the Southbridge and October 22 for the "RAID" drivers which include the AHCI drivers you are looking for. And I should add that these drivers are very recent.
.....now.... There *have* been reports of poor AHCI implementation with AMD, which even includes the new SB8xx, but that is a different topic, and I personally have never had a problem with their AHCI, though I would go with Intel's ICH for mission-critical applications.