I should also mention that the RT approach isn't the holy grail either for time sensitive robotic control systems. Read up on the Pathfinder/vxWorks priority inversion bug if you'd like to see how hard deadlines can sometimes cause more problems than they solve...
priority-inversion is well-known and easily coped with.
Hard real-time, deterministic code is simply a prerequisite for safety in these types of systems, you have to be able to reason about how your system will behave in worst-case situations.
