I don't think good-bye threads are dramatic or people looking for drama. I think over time you do form a bond to certain posters, if you are lucky, lots of other posters. It really wouldn't be fair to just drop out on your friends, and one post is a lot easier than a lot of PMs.
Some need the closure, they need to say, I needed this place and I grew here but now I need to move on. Its healing to state that truth and let others hear it.
I don't see the need for sarcasm or rudeness about it, the fact that others think thats necessary makes me think they may have a little self esteem issue of their own or anger issues or abandonment issues. The good-byes aren't posted for their benefit anyway.
Sherry