Deaths were going to happen with this event no matter what, this wasn't your typical tornado outbreak. I've been chasing for nearly ten years and looking at the speed and coverage of these supercells, I wouldn't want to have anything to do with chasing in that area yesterday.
Looking at all the technical data on radar is one thing and its easy to say why didn't these people just leave town? I don't know how many people have actually seen violent tornadoes in their life on here..But they are unpredictable in the field, radar might show one thing. But when your actually face to face with one it changes within seconds.
For example, the tornado in my avatar is one I caught back in August 24th 2006 in MN. It was an EF-3 multi-vortex that grew to 3/4 of a mile wide within 5 minutes or if not less.
Tornado deaths are unfortunate, but its mother nature and its going to happen. You just have to respect that.