How would you feel about modifying Dark Heresy so that it uses a roll over system rather than a roll under system (i.e. you have to roll d100 + your skill and hit 100 to succeed)?
It would be completely pointless.
because thanks to the margin-of-success rules you don't lose any amount of complexity by inverting the rolling system.
Actually, I would say you do--less head math. Subtraction is much harder for most people to do in their heads (in my experience, at least), and if you roll over 100, you simply need to drop 100 from your roll to figure out your degree of success.