why can't the blu ray and hd dvd groups work together?

there must be a way for them to work together to make a universal hi def dvd. why aren't they developing a dvd that's using the same technology as standard dvds?

You've asked a mouthfull. I'll answer the easy question first. The reason why HD DVD and BLU RAY Discs are not developing a movie format that uses the same technology as standard DVD's is because standard DVD is an old technology. With HD and Blu Ray one can store much more data on a disc when compared to standard DVD. Blu Ray and HD are the future.
The reason why they won't work together is that they both want to be the standard for Hi Definition. There's a lot of money to be made in this market. They both use similar technology, where they both use blue lasers, but Blu Ray has much more storage and use capability, whereas HD just has enough room to hold a movie in High Definition. But they won't work together because they're too differant, and they both want the monopoly.