You say yes, I say no. You say stop, I say, go, go, go!
OH NO-OH
You say goodbye, and I say hello!
Sorry, couldn't resist. Anyways, the main reason is that leaving should just be kept in you blog, since people come and go all the time. Plus, not everyone has to know about your leaving; if it's in the blog most likely only your friends, i.e. people who care, will see and that's everyone who really needs to know.