And this is exactly why they generally don't. If something happens that keeps it from happening, people say "But you promised it in this thread right here. See that thread, they said it was going to happen, but it did not! OMG IPS IS HORRIBLE! I can't do my new site and the world is ending... oh what a world, what a world!"
OK... so I'm being a bit sarcastic there, lol. However when something happens that keeps a date from being released, people tend to freak out. As someone who deals with managing user exceptions at work, I know exactly where they're coming from with being reluctant to give any kind of dates.