I completly disagree, and i have never met anyone who is impervious to being smacked in the nuts. krav teaches more than one way to get out of a headlock anyway. and sorry to hear about you getting jumped man that seriously sucks
Then you haven't met the wrong kind of people. Have you ever tried to fight someone on methamphetamine, crack or really drunk? How many live encounters have you been in (not in the academy) where you have used a "smack in the nuts", and have any of those encounters--if there are any--involved your opponent under the above influnces.
I have personally dealt with all of the above. Some times, yeah, groin shot works, often, no it doesn't. I have told a story on here before of being, what some might consider, seriously injured in that area before--and still working as a doorman for sometime before noticing that blood was dripping down my leg! I went to the bathroom and lo-and-behold, there's my testicle...I could see it through the hole in my scrotum.