Interesting point, but it fails a number of crucial tests:
⚫ The spec isn't code. More to the point, it's not a derivative work of Markdown itself. The BSD license applies to the licensed work as a whole. What it doesn't apply to, specifically, is other works which refer to the original. That is: copyright is not trademark, and you cannot embed an effective trademark license within a copyright license.
⚫ Works (parsers, libraries, etc.) based on the Standard Markdown spec which do not incorporate any of Gruber's original Markdown code are themselves not derivative works of Gruber's original BSD-licensed work, and again, are not governed by the license.
⚫ There are a number of things copyright doesn't apply to: functional works (SEGA v. Accolade), simple compilations of facts (Feist v. Rural Electric), and APIs or standards (I'm aware of a few cases involving these, though I don't recall specifically if any are precedent). Specifically, however, a copyright license cannot cover facts or functional design. It only applies to a specific expression of an idea. Paraphrase that idea and you're scott-free.
So while you raise an interesting point, it's moot here.