That you'd ignore an "exit post"... bwahahahaha!
I agree. The idea of "leaving in a huff" and including some "venting of frustration" in a farewell post has never led to any positive result; and is categorically just a bad idea. It seems that "making a quiet and inconspicuous exit" is likely the best approach for forums. Not necessarily because it's a good method, but rather it seems to be the least bad.
I simply dislike decisions based on evaluating options based on the "least bad". Sometimes, there simply isn't an alternative, though. I'm not without hope, however. Eventually, someone, some day, on some forum, will make a positive "farewell my friends" post to "be the exception the proves the rule".