If you're going to make a movie about your old high school experience, why would you keep a few names the same without getting some permission? This especially becomes a problem when the fellas think of themselves as mature and respected, where you've portrayed them as "dazed and confused." I'm not sure what would have been lost by changing the names, and maybe Richard Linklater wouldn't be getting sued.
But it seems like quite a long time after the fact to be bringing it up, doesn't it? Still, it's a really funny movie.