Why do people pre-order DVD's?
It's no like their going to sell-out, is it?...
This question comes up a lot and here are my answers:
1) In the case of Indies (like Troma), preordering is a way for retailers to gauge interest in a product. If a lot of people preorder a product, chances are, that retailer will stock more of said product. (I realize that's not the case with DK, but it's still a valid reason)
2) Freebies. Many retailers give you a bonus toy, code, download, whatever, for preordering.
3) Piece of mind knowing you don't have to stop at the store and get it. I know this isn't a big deal for some people, but for many, a stop at the store can really feel like a chore.
4) If you preorder from Amazon, you are guaranteed the lowest price. DK Blu-Ray showed up in my personal gold box on day at the fantastic price of $22.99. I preordered and also have a guarantee that if it goes lower, they will adjust the price. I also get free 2 Day shipping with Amazon Prime.
Those are all just my personal reasons, I'm sure other people have other reasons.