I think the reasons for sending out screeners in SD on DVD, at least from Hollywood, are are multiple; first is guaranteed universality at the lowest common denominator, second, an SD image with constant bug and L3 warnings is very slightly less fodder for piracy, and third, price per unit is cheeper, which matters more, since there is no recouping costs on a promotional item. Basically, there just isn’t any real incentive to change the process.