I think this is a crux here, but I don't see the validity of the criticism.
I mean theses expos are really just fan service events, and if anything free focus groups. They aren't general marketing events or PR type features. The people who are taking time off of work, and spending money to go to events to listen and talk about Disney are both 1) already fans of Disney and likely have and going to again vacation at Disney no matter what, and B) very small minority of Disney's overall customer base. To the vast majority of the people who vacation at Disney, they have never heard of these expos, and have no idea what is said at them. These expos are for hard core fanatics, message board people, DVC people who are locked into the Disney experience.
The real "announcements" and PR for new rides features, lands, ect., aren't part of these fan expos. They are part of the holiday special on ABC, which has lead ins the week before on all the ABC affiliated morning shows. Or they are part of some other prime time feature special geared towards the main stream general public. If you read these message boards, after those specials, more times than not you see pages of commentary about them not containing anything "new."
What I think people don't recognizes is that for most people the information there was new to them. Most people, to the extent they know Haunted Mansion is getting something new, didn't hear about it at the last Disney Expo, so they aren't dealing with the so called log delay in announcement to construction.
The expos are glorified gab sessions. They aren't scheduling conferences and they aren't binding. It's not a sham to announce your going to do something, and then do it, but do it on your own timetable. It's also not a sham to say hey, we are thinking about doing this, and then change your mind later on.