Re: Using d20 instead of 3d6 (DON'T KILL ME!)
Or that they are not talking about a rule set and are talking about using a 20 sided die that is used instead of three six sided dice for use in Hero System.
As for d20 system, since it is licensed those who obey the System Guide are d20 products. So the only real "base" is the character creation and application of experience towards advancement, which is only obtained through WotC books. Everything that is in the SRD is for reference and can be changed and still have the official d20 logo. I am only putting this in since you talked about "actually learn and speak correctly about a rule set" which in its very nature is undefined with the exceptions about creation and experience.
I personally don't have a problem with d20 system but since the only standard rule set within it deals with character creation and experience it is difficult to "speak correctly" about other rules that are officially licensed as not being apart of the d20 rule set. So the rule set for d20 is, by its nature, for the most part undefined. I am not suggesting that we "undefine the term d20" I am suggesting that since it is already mostly undefined that we should define what aspect we are talking about for greater communication.
So if someone says that d20 System has automatic failure for skill check on a natural roll of one they are correct. Just like someone is correct when they say that d20 System doesn't make a roll of one an automatic failure for skill checks. So lets all please try and learn to talk correctly about d20 System and its rule set.