I don't understand why more vendors don't do this (if anyone wants to comment to this, I would be interested to get another opinion.) While my experience is admittedly limited to obscure chips that require NDAs for access to the specs, I was always a little annoyed that almost every time there was not even a reference to the errata documentation that the vendor provided when a new version of the spec would come out.
Now in AMD's case, I would argue that they should be more clear that it's an errata, and mention that the updated spec differed from previous versions (which it alluded to by saying "This behavior is model-dependent".) Ultimately, the spec is THE document on how a user should expect the chip to behave. So sue me if I am blurring the lines between an errata and a mistake in the spec, but I just want my documentation to tell me what the chip does without having to refer to a dozen other secondary documents dang it!