Palm heel strikes, both with fingers retracted and with fingers extended, disguised as a spearhand; face claw-strikes with spread fingers aimed at the eyes; flat-hand slaps to the ear/temple; half-fist strikes (open hand, fingers bent so the middle knuckle is the striking surface, aimed at the throat, spearhand to the base of the throat... and more... are all part of the technical repertoire of TKD. We train them and we practice them.
This isn't a function of the system per se, it's a function of how you train, no? There are ways to get powerful leg muscularity and considerable speed that don't depend on training low, and if you watch some of the top TKD competitiors, you'll see as much speed as you could want. And I say this as someone who has no interest in sport TKD.
Again, I think you're talking about training, and how people choose to spar. If you're training TKD for street defense, you aren't doing anything like kumite or standard sport-TKD sparring; you're training application of the system to defense against grabs, roundhouse punches to the head, head-butts and other typical violence-initiators. You aren't having fun, or being especially `friendly'; you're practicing throat strikes with knifehand and forearm, strikes to the face, pins to control the attacker to set up knee kicks to the abdomen, and elbow strikes to the face (and, if the attacker's head can be forced low by a controlling move based on a wrist or elbow lock, to the back of the neck as well, which will most definitely end the fight). This approach to TKD is certainly traditional: it was the fighting system of the RoK military in two wars, and was fearedwith good reasonby the South's communist enemies (see this for more detail and documentation). So far as I know, it's the only variant of karate (I consider TKD to be the Korean development of Japanese karate, just as Shotokan or Wado-Ryu are Japanese developments of Okinawan systems, themselves syntheses of Chinese chuan fa styles, native combat methods and Japanese samurai bujitsu theories brought over by the Satsuma warlords) ever adopted as the battlefield combative training for an entire national army. The technical resources that made TKD so damaging are still part of its content. And as for conditioning... a lot of experienced TKDists train their force delivery via multiple board breaking; the strikes those TKDist are able to deliver as going to be perceived as anything but `fun' and `friendly' by anyone unfortunate enough to be on the receiving end of one of them.
I think part of the problem is that there is a systematic ambiguity which arises when ever you use the name of some particular martial art. That name denotes a set of techniques, and a theory of combat often (though not always) encoded in formal patterns that integrate these isolated techniques as applications of certain strategic principles and tactical methods. But the name also identifies what you might think of as the current `state of the art', including how that art is trained. There's plenty of soft TKD training that goes on; but that's true for Shotokan as well; read anything by Iain Abernethy or any of the other British Combat Association karatekas, and you'll notice that time after time they compare the `alive', unscripted, realistic training with totally noncompliant partners they advocate with tradition kihon/kumite-based training. The two cases are very similar. Take someone from a `hard' TKD school, say one of the Song Moo Kwan dojangs, and compare them with someone from a Shotokan McDojo, and the picture you paint will still fit, except it will be Shotokan which is `fun and friendly' and TKD which sends its practitioners home with major bruises, or to the doctor or the emergency rooms with fractures.
What I'd like to do is eliminate this variable, the different approaches to training, from the comparison, because it's not an inherent part of the technical content of either art, and therefore will give a distorted picture. It seems to me far more productive to compare, example, how each of the two arts equips a skilled practitioner to handle a series of commonattacking moves by an untrained, but dangerously violent assailant. A roundhouse punch is thrown at your head, with or without a set-up grab: what do you do? That sort of thing. I strongly suspect that if you do that sort of comparison consistently, you'll find little difference amongst Tang Soo Do, Taekwondo, Shotokan, and maybe a couple of other styles.
It would be a very interesting and useful exercise to carry out, but to do it right, you'd need a number of practitioners at the same advanced level of training, and a couple of days to experiment with how they responded to `live' attacks (by the same group of ukes, to control for as many variables as possible). In the absence of that kind of relatively controlled experiment, a good deal of all all this discussion probably has to count as somewhat-informed guesswork...
