[Blarg]

Those are the targets you specifically train for by doing the exercise. You get to those targets by going through and around the natural or practiced defenses someone has, and through their offense. That's what those exercises do. They're not about moving your arms together. That is a popular misconception of what those exercises are about. They are actually very goal directed, not about themselves.

A tai chi or wing chun man has zero interest in doing pushing or sticking hands in a fight. It's a very competitive training exercise, and a great one. But he merely wants to whack you one. The place for sticking comes in only when the attempt to whack you gets interrupted by the establishment of a bridge, that is, contact between your limb and an opponent's limb. You don't seek it out; you'd rather be whacking someone. But these things can happen. You just want to get the interference out of the way and start whacking, and the exercise is a competitive way of dealing with trying to do that so your own strike (or throw) gets through. But you don't hang around doing sticking for fun. Your object is still to punch or poke the guy or whatever. And in learning by contact, by feel, instinctively how the body and its limbs move in offense and defense, and competitively trying to take advantage of that knowledge, someone practicing sticking is constantly training in getting through. The eyes are the highest priority, but actually you are training to instinctively respond to all openings the moment they occur. The whole thing is ultimately working toward the strike, and past active and determined opposition.

Properly defending vital areas is easier said than done, just like hitting them is. But people do train intensively to hit them and practice it constantly. It will always come down to who is the better man, though, not who knows more techniques or ones he presumes are better. If you know the best techniques but the other guy is faster or has better timing, or is just in better condition or has higher pain tolerance, you may well lose. Technique is just one part of the equation and sometimes not the one that matters.

I'll grant you that groin kicking is surprisingly hard, as there are very strong instincts to protect that area. And that it is very possible to fight on after being kicked in the groin. I have. But if you can get a hand to the head area at all, you need very little speed or power to reach the throat or eyes and do damage there. The tricky part of course is getting the hand through to the head area. Once through, you can often do what you want. Including go for the eyes or perhaps the throat. I've had many a sparring clash come to an end when my fingers were clamped on someone's nuts, around their throat, or drumming along their eyebrows.

Regarding tae kwon do, being an art for applying at a distance, and an art that generally puts you on one leg, it is indeed useless when someone's on top of you. Wing Chun is one of many that actually favor close in fighting, though, as do all systems that teach a variation of sticking. Different styles of course work differently and are stronger in different ranges.