Have you ever worked in a software or video game store? I did for a couple years, the amount of hate and furor I heard on a daily basis from people when they found out that the game they want has been pushed back was unbelievable, and just about every date we received that was more than about 6 weeks out would get moved at least once. The few times games came out without delays, we instead got to hear all the hate about how buggy and rushed the end result was; just look at some of the conversation in the thread going on about the interview with the guy from Obsidian, with people still complaining about how KOTOR 2 was rushed and buggy, and came out 10 years ago. You also get to hear about all the games that got delayed and how they weren't worth the delay, with examples like Duke Nukem Forever and Battlecruiser 3000AD. The release date announcements generated a lot of hype in the media, but they also generated a lot of angst and negative feelings among the customer base. On the other end, it was pretty common for people who didn't know anything about the release schedule to come in and be very happy and surprised when they see something new on the shelves.
Release schedules also generate traffic spikes at your retail outlets based on the release dates where a flood of people come in on the release day to only get the new product and get out as fast as they can, as opposed to stopping by regularly to see what is new and occasionally picking up something else in the process. These spikes are not necessarily good for the retailer; although they do get a sudden influx of sales at release, there is the chance that the reduction in regular browsers stopping by to see what is new can reduce sales overall, and those release crowds can drive away customers who aren't there for the new release. I remember working the day the N64 came out, anybody who wanted anything other than a N64, games, and accessories were going to be waiting in line for at least half and hour, and hopefully the customers didn't have any questions because every worker was busy either unpacking the shipment, getting together the preorder, calling the preorders, or running the register.
As soon as you put out a release schedule you will have a certain subset of your customers who take it as an unbreakable promise and will throw an absolute hissy fit if anything changes. We've seen it here with the reaction to the changes to the Adventurer's Handbook, and that wasn't even on a publicly announce release schedule, it was something leaked through a distributor. There are a tremendous number of variables involved in publishing, not all under the publisher's control. You may have art or freelance writing come in late, additional unexpected edit/rewrite cycles, unexpected legal issues, financial issues, even issues with printing and distribution. Printers aren't sitting around idle waiting for WotC to send them the book, they have schedules lined up well in advance and a minor delay in getting the book to the printer may result in a long wait until the printer has a gap in their schedule to do the printing. If you go with overseas printers to save costs, then you introduce the chance of delays in shipping or in customs. It is far safer from a business and PR perspective to wait until fairly close to the actual release date to make the announcement to minimize the chance that the date will have to be moved.
If you want to encourage WotC to give more information about their release schedule, don't fan the flames of rage when something gets changed or delayed. If you see a fellow poster getting wound up about a delay or change, try to calm them down and help them keep things in perspective. A four week delay in a book's release is a minor inconvenience, not a life altering change; it's not like lives are hanging in the balance or customers are going to lose their jobs because an RPG book got cancelled. This is a game we're talking about, civilization as we know it will continue just fine even if there were never another RPG product published. As long as there is a rage storm every time a change is announced, I can guarantee WotC will remain shy about releasing information. If they think the vocal elements of their customer base will be more understanding, they may just become a little more free with the information.
