don't answer that last ask I sent you actually. a) because I've since realized you rightfully don't give a shit about wizards of the coast, and would be justified in deleting the info I wanted from your brain as soon as you learned it, b) because I realized you aren't Google, and c) because I Googled it and found out myself.
on a related note, did you know wizards copyrighted the term "d20 system??" wtf. that was the last place I expected to have problems. I thought it'd be, like, "armor class" or "difficulty class" or something else similarly oppressive and cruel to copyright that would force me to change my whole rules document, and mess with my player's ability to remember which mechanics have had their name changed.
Somehow copyrighting the term "d20 system" feels even wronger than that.
Wizards of the Coast is the outfit that popularised the idea of categorising game systems according to the shape of the dice you roll in the first place. There are a few prior examples of games with similar naming conventions, including West End Games' D6 System – which is where WotC probably got the idea – but the idea of "dX systems", where X is the shape of the dice you roll, as coherent categories of games is very much a post-d20 System phenomenon.
That is, it's not that WotC trademarked (note: not "copyrighted") an existing piece of in-use terminology when they trademarked the term "d20 System"; it's that the idea of lumping all game systems which make use of twenty-sided dice together under the category of "d20 systems" was popularised by WotC's trademark.
(Indeed, if one were feeling conspiratorial, one might observe that the idea that all systems which roll the same-shaped dice are basically interchangeable with one another is a notion whose popularisation has proven very convenient for WotC's post-3E marketing strategy!)
