Mike,
I have discussed this with our track marshal and we have agreed that while the left side is pretty well inside the frame, the right side certainly sits out far enough to require some kind of extra protection. It may be hard to hit it if you have good rear sets and clip-ons, but if one of those things fails (and they fail pretty easily a lot of times) it can grind the case down and we are both more comfortable making the right side mandatory for the 250