Why there are so huge differences in prices of the same DVD?

[Adrian20XX]

Hello,
I'm going to buy my first DVDs to improve my game, and I'm absolutely atonished by the price differences that I find on what seems to be the same item.
Can anybody explain me what is going on here?
For example, let's take World Poker Tour Season 1.
I use pricegrabber.com to compare the prices, and it costs:
* DVD Empire: 35.71
* Amazon MarketPlace: 48.98 (price of the new ones, not used)
* CD Universe: 55.69
* Digital Cranium: 59.99
* Amazon.com: 71.99
* Discovery Channel Store: 79.95
It also costs at Buy.com 71.99
Any help will be appreciated.
TIA & Regards ...

[Precision1C]

It is a retailer's job to maximize their profit and your job to pay the minimum price including expended time and miscellaneous hassle. Just buy from the cheapest reputable dealer or not so reputable if you like extra risk and you have done your part in lowering prices for everyone.

[Ron Burgundy]

Make sure you include shipping.

[ECDub]

Your buying World Poker Tour DVDs to improve your game? Start with WPT Season 2...at least player commentary is included on a few episodes that will help your game.