In defense of shrinkwrapping (I'm not taking a stand here as I see the positive and negative reasons):
1) I've heard groups of D&D players who commented that they never bought any modules. If they needed ideas they'd just go to their local game store & look through the adventures for ideas. No need to buy anything when it's free to look at.
1a) Cheating players would leaf through the adventure they are running through at the store to find out what was happening. Admittedly, this is a minor reason. However, it adds to some people's temptation.
2). I've personally bought gaming materials at a store where someone was obviously going through the books while eating a chocolate bar in their hands (I hope). Large smears of brown material in sections of some of the products. This wasn't just an isolated occurance, either. Needless to say, after something like this, you'll be pissed at the store for some reason...plus you'll look thoroughly through any product you buy that isn't shrinkwrapped. I'm sure stores lose a lot of salable prodcut because of things like this.
3) I know of another case where there was a store that made sure they had non-shrinkwrapped material. Much of the product on the shelf had that "used" look from all the leafing through that was done. If they had no copies in good condition, people would look through it & go to their competition and buy the pristine shrink-wrapped copies.
Glyfair of Glamis