The difference between Harry Potter and Star Trek or Star Wars is that JK Rowling isn't milking the franchise the way Roddenberry or Lucas did. She's shut down future production, says there's no more sequels, no prequels, and she's moved on to other projects.
If she'd decided to write a prequel series about Dumbledore, and authorized a Hogwarts cartoon series, you'd be seeing new Potterverse for the next 2 decades easily.
Potter has had easily as much cultural impact as Star Trek or Star Wars, and I'd argue that in it's time frame it has had more. Toys, Hogwarts robes, action figures, board games, video games, but more than that, just mention "Dumbledore" or "Snape" to someone, as in "My professor follows the Snape theory of teaching" and anyone will immediately get what you are talking about. That isn't true of the Matrix, it's not true of Twilight.
I'd say "tier two" would be Buffy; most people would understand a reference to the main character, even they hadn't paid attention to the show, and the show had a huge impact on what came after. I'd argue it spawned Twilight and to some extent the Zombie resurgance; it made the undead cool and interesting.
I think the Marvel universe could be argued as being bigger than Star Trek, Star Wars or Potter. Active since the 60's, it caught the attention of college and university students when comics were just for kids. It's covered every medium. Paul McCartney wrote songs about it. There are conventions with fans dressed up in costume. Why I would put it ahead of DC is because Marvel has marketed the the universe through the latest movies, all tied in and leading to the Avengers, which DC didn't do. The universe is a coherent whole even in minds of the casual viewer. Meanwhile they successfully market the coherent universe to kids as young as 4 with Super Heroe Squad. I think they've pulled off the integration of their entire universe into the mass market and varied media in an increadibly successful way.
That doesn't mean that their movies, comics, or action figures are the best, but I'd argue they've put their world into the minds of more people, more successfully.