Stepping out of bounds seems to be a poor justification for the loss of a significant amount of points in the Olympic gymnastic floor routine. It's good to have a boundary, and they should tell the girls to use the boundary as their guideline for movement -- but it shouldn't count against them to land a little outside of the line. I can't imagine how you could accurately calculate precisely where you will land after various flips and spins in the air, or why that would be expected, or even desirable.
Plus, keeping a strict boundary favors very small people -- you know who I'm talking about -- since they can do more within a smaller area. Rules should be about leveling the playing field (see goal tending), not skewing it.