[Null]

a few reasons.

the few i have and have seen with both on it, have it on both sides of the disc, one is wide one is full.

reason 1. people actually like seeing a graphic on the top of the disc rather then both be a data side. more appealing to people.

reason 2. space, ones i have with both formats on the same disc dont have much in the way of special features. not a big reason, but it plays a part in some ways.

reason 3, the main reason... Money. theres a number of reasons why they get more money releasing both formats.. one i always argue is that everyone buying full screen now because they dont like black bars... will end up rebuying movies in widescreen years later when hdtv's become standard.