Quoted from PinballTilt:Redbox surely does have control over this. With the amount of movies they buy they could get the studio to do anything if they were willing to pay for it. Most likely they negotiated a lower price per disk if they don't come with bonus features.
I'm sure this is exactly what happened. And likely not to gouge anyone. As someone mentioned, Red Box probably won't be around in 5 years, just like Blockbuster.