Now, before I answer, I am going to ask that people not look at the word in a literal sense.
The answer?
Based on what I've seen in many years of kumite, both as a participant and obsever, it comes down to a matter of different strokes for different folks. Different guys have different sensitivities in those nether regions. With some, it only takes a very light tap, and they get nauseous. With others, it might mean taking a more direct shot.
Regardless of the levels of sensitivity, though, a direct hit to someone's testicular areas does hurt, and will at least slow someone down, unless that person has a total lack of nerve endings there. I don't care if someone follows the Jukokai methods; what people get hit (or more precisely, where) with in combat versus demonstrations are two different things, indeed.