I think that there is a level of intellectual dishonesty that's going on in this discussion that unfortunately is typical of nerd fandom and people who have to be right.
The OGL has it's origins in the idea of open source software. Because this is closer to what we're actually dealing with than "Kleenex" or "Frisbees" because of how open source software and the OGL are used.
There are several different distributions of Linux.
Debian, OpenSUSE, Unbuntu, Fedora etc. But they're all Linux at their core.
No one is going around saying that Unbuntu is Debian becuase they are both Linux. Or that Fedora is OpenSUSE because they're both Linux. because that would be dishonest.
But again all of these distributions are Linux. That much is in agreement.
Linux = D20
Distributions = D&D, Pathfinder, Mutants and Masterminds, Star Wars (SAGA), etc.
I play Pathfinder. I DO NOT play D&D. I do not call D&D Pathfinder. I do not call Pathfinder D&D. Are they both D20 based systems? I guess, since I havent played 5E, but I'm assuming that it still has it's roots in rolling a d20 to hit a target number. I dont call Mutants and masterminds D&D either, nor do I call Star Wars Saga D&D because it's not.
The Pathfinder iconics are the Intellectual property of Paizo. For the same reason that Pazio CANNOT do a Pathfinder version of AGE OF WORMS or SAVAGE TIDE because those two AP's are the intellectual property of WOTC. It's dishonest and flat out wrong to claim anything to the contrary in order to win an argument.
Does Pathfinder, Star Wars Saga and Mutants and masterminds all have their origins in the D20 system? Absolutely.
Are they D&D? No.
Now and this needs to be said, I have no problem with if among your group of friends or in your town it's all D&D because that's what you've chosen to call all RPG's. I get that.
But to argue and insist that this is a universal truth and should be acknowledged? Yeah...NO.
When I was younger (especially in the 80's) we described everything as "it's LIKE D&D except with spaceships and aliens (Star Frontiers). It's like D&D except with cowboys (Boot Hill). It's like D&D except with spies (Top Secret S.I.)." But now with the pure amount and variety of games out there I simply call a game by it's ACTUAL NAME.