I figure it's best to give out as much information as can safely be done as soon as it can be done. That's what tends to underpin how I answer that question.
I've worked in Customer Service and/or sales a lot, and coming from that standpoint, I tend to agree with you. Even though, personally, I'm fairly impatient, I think that warning us about the impending change is better than just dropping it on us and making it seem like it came out of nowhere.