My understanding as far as why products have specific release dates has a lot to do with some kind of fair retail act agreement that most companies agree to honor. Basically how it works is a manufacturer will put a specific date of release on a new product, despite them shipping it a week or more before that date. Some retailers may receive the items much sooner than others, but are supposed to agree not to put the product on shelves until the date specified to ensure all retailers have the product in-hand and in-stock to sell. That way there isn't a system of "favorites" going on in which one retailer is able to monopolize the market on a specific product because they got it first and are able to sell it without competition. Of course, as shown in this thread, companies often don't bother with waiting.
There's a myth (often told by Gamestop employees) in the video game world that they (retailers) will be "fined" by a publisher if they put their products out for sale early. This is largely a myth, because although a publisher could attempt to impose a fine if they wanted to, there has not been a true recorded instance of it happening in history, and there is no real obligation for a retailer to pay it. Sure, Activision could attempt to "fine" Wal-Mart for laying those copies of COD out a couple days early, but what regulatory agency actually exists to make sure Wal-Mart pays? Certainly not Interpol or the FBI. The truth is, if Activision really wanted to seek damages for this, they would have to sue Wal-Mart in a civil/business court. Activision would most likely pull their shipments from Wal-Mart stores, WM would respond by banning their products from the stores anyway, and the end result is you have Call of Duty games going out on a much more limited release campaign. In this situation, it's easy to see that everyone loses. To keep the peace, retailers will generally try to conform to the street date standards at the strong insistence of the publisher. But to be clear, the whole thing about fining a GS store 10,000 dollars or whatever is BS. It wouldn't surprise me though, if GS execs told their employees that to keep them from thinking about doing it.
Here's an article about why breaking street dates are not good for the retail industry (it specifically talks about video games):
http://www.kotaku.com.au/2011/10/why-street-date-breaks-are-bad-for-the-games-industry-as-a-whole/