It appears that WotC is attempting to make that distinction in the portions of the claimed PI and OGL quoted in Ben's post at the top of the thread, as set apart from their more common usage in the text of the SRD refering to "(d20)" as a "twenty-sided die".
Not when we get to the point of whether or not WotC is also claiming "d20" as a trademark.
Not precisely. If WotC is making the claim that "d20" is a trademark as it refers to the system, and since the OGL has always had separate restrictions on trademakrs, then it was never truly open content...as it refers to the system, though it's more general usage as refering to a twenty sided die could very well be. That's the distinction I believe that they are trying to make and the reason that this conversation is not simply about PI but also involves trademarks.
Personally, I am not in a position to challenge that supposed distinction, nor am I inclined to do so if I could.
Nevertheless, it seems clear to me that aside from their specific instances where they have delineated the usage of the d20 logo and appropriate accompanying text phrases, they are not interested in allowing folks to claim closer compatibility through the use of such things as using "d20" within th name of a product or other such refering to the term d20 as it refers to the system. As to use of it to designate the type of die to cast in a given situation, that seems to be acceptable under their terms.
Further, isn't it true that anyone who uses the OGL (with or without the d20 STL) in it's current format is contractually accepting the terms of that license on face value and thereby decreasing the strength of any challenge they might make at a later date to any of the specifc terms of said license?
Again, not a lawyer and just throwing my reading of it into the ring but in this case separating trademark discussions from PI discussions do not seem possible as it appears WotC has intertwined them.