It is a distance thing. If you are close enough to fight chest to chest, that is exactly what you should be doing. If you are far enough away, that you have to worry about missile attacks, you need to minimize your targets. I don't believe it is an either or, thing.Oh no that's not fun! Are you ok now?
That's great that boxing protects what their stance exposes, my statement is still true though that the boxing stance does expose your centerline. It's not the only stance that does this but it does. In my opinion I'd rather make it easier on myself by keeping my center line away from my opponent, then exposing it and having to worry about defending it.