Why do they want to change the DVD format to Blue ray or HD-DVD format ?

blue-ray and HD-DVD are high definition formats that have better picture and sound, a regular DVD doesn't have the quality to take full advantage of todays high def TV's you can still use your old DVD's and VHS tapes and you can still buy cheap devices to play them. If you are the type of person that always has to have the latest and greatest stuff then you can get the better quality but it will cost an arm and a leg. There are always people who are willing to pay anything to have the best system out there, so the electronics companies are always scrambling to make something better so they can get money from these types of people. .

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To keep the copying down. It takes a few years to come out w/a burner to a new format. If they keep changing it, then it's less of a chance people will be able to burn it.

I really like the above answer, I'd agree with a lot of it. Basically companies are putting out HD material because there's a market for it. TVs can go up to 1080 lines of resolution, so why shouldn't home video? DVDs simply can't support it space wise, so a new disc is needed. Hence HD-DVD and Blu Ray. Do you have to buy it? No. In fact, it remains to be seen if HD formats are nothing more than niche markets. A lot of people are fine with what they have, and I don't see DVD going away anytime soon. Remeber it took a good 5-6 years before DVD overtook VHS. And that time frame will likely be much longer for HD formats to overtake DVD. There's also the idea of diminishing returns. I'm not sure what's after Blu Ray/HD-DVD. Downloadable movies have been suggested. That may happen. But you reach a point where more disc space doesn't really matter. More resolution can't be noticed by consumers and/or handled by TVs. So I expect there to be some longevity to these formats as well.