I suppose it isn't, but I bristle when I see someone tossing around statements like "close enough doesn't really exist". In my experience when statements like that start up, there are people involved that don't understand variation is a part of every real process. My point is that if you're going to get into safety critical systems, there is always going to be some amount of variation, and there is always a "close enough", as there is never an "exact" in real systems.