It's the new mythology, as we talked about before. Superman's old news (no pun intended toward Clark), X-Men is 30+ years old and the third movie. People are hungry for something new which has enough familiarity to it that it does not alienate them - hence the popularity of POTC. Everyone "gets" pirates, they pillage, they plunder, they're greedy bastards. And fun as hell. What's not to love? And Johnny put a twist on the whole thing which makes that fringe audience you mentioned grin with glee. I believe the rest don't have a clue about the slashiness of it all - they just think he's a drunken pirate.
Truthfully though, the Disney name behind helps some too. Family people think it's "wholesome" entertainment.