Can someone tell me why retailers release a 1-disk version of a movie for like 28 bucks and then release a 2 disk for 30 bucks? that makes no sense.

So they can buy bigger houses and more expensive cars.

Walk The Line is $10 difference between the two versions, and only very few extras on top of those already on offer in the one disc. Explain that??  

The reason whu is that when a new movie like "Walk the Line" comes out Wal*mart Circuit City sell them at a loss. Walk Line wholesale price for the single disc editon is about $18.50. They sell them anywhere between $14.99-$16.99.  That is a loss. However they regain there profect from 2-disc set. They only  mark them down 20% below MSRP. Please keep in mind the sudios know most people prefer just the movie and do not want the extras.  That is why there is dual release at the same time! This "dual release" will get more rapid as time goes by.  The DVD shelf space at stores is limited this also explains  another reason for the dual releases.