Same is true of Hacker News or, really, any other community group that involves writing and is populated by intelligent, articulate individuals (Reddit, Digg, I'm looking in your general direction).
Moral of the story: Write more and have people read and critique your writing.
I'm not a native speaker of English, I've studied the language for seven or eight years, and a couple of months ago I signed up on Hacker News and Reddit. I've learned a lot about establishing strong and rich discussions by reading and writing comments and messages. Generalizing, this idea could be boiled down simply to "practice is good." Of course, all the years I took formal English classes were very useful, but we must not underestimate the power of putting our knowledge to use. Theory without practice is meaningless, knowledge without use is, well, useless.
Moral of the story: Write more and have people read and critique your writing.