A company (Warner Home Video) has actually come up with a hybrid of both (for just such an occasion as when a distributor wants to cater to both markets without coming up with seperate discs). Click
It works because the data layer for a blu-ray disc is closer to the surface of the disc then the data of a HD-DVD disc (0.1mm and 0.6mm respectively). I can't remember the name of the company, but what they've done is basically put the blu-ray data onto a layer that works like a two way mirror. It's reflective enough that the laser of a blu-ray player can access such data, but transparent enough that the different laser of a HD-DVD player can access the data beneath that, which will be the same information, but encoded to work with a HD-DVD player.
If more distributors dealt with their products like this (currently only Warner Home Video and Paramount support both formats) it would make things a lot easier for those of us that don't want to choose, and the format war would be won by whoever sold the most players instead of whoever sold the most discs.