First off, while this is a subject I've thought a lot about, I certainly don't have first-hand knowledge, so a lot of what I'm saying is second hand and / or conjecture. Second, I'm pretty sure a lot of the teas you have in the second section (HK high-fire) are not from / roasted by HK shops. However, the stuff from tea shops in HK that have been around a while (Lam Kie Yuen, Lau Yu Fat, Cheung Hing (Xiang Xing), Best Tea House, etc.) does have a characteristic style and taste. The folks running a lot of these stores are from Chaozhou or Fujian, and sell to an audience that still likes the older high-fire style of tea, and is willing to pay for it. Who knows what will happen when these folks retire. In the next paragraph, I'm talking about these teas, but not necessarily most of the ones in your second list. Certainly, you would be well-advised to talk to Michael and / or Tim, who probably have more direct knowledge than most people who post here.
To me the difference is that the firing is more aggressive, and the HK shops tend to rest it longer before selling it. The HK shops tend to buy the tea as maocha and then roast it to their own specifications, and I am pretty sure a lot of this tea has a good healthy dose of oxidation, which may partially account for the sweetness and characteristic taste these teas have. I've heard that they use a "recipe" to keep consistency from year to year. I would guess that the "recipe" includes the type(s) and oxidation levels of the maocha itself, the length of each roast, and the time between roasts, as well as the period to rest the tea before selling it. Some of these shops have been open for quite a while, so the roaster may have quite a bit of experience, and I would guess that they have some sort of long-term relationship with wherever they get their raw material. I am personally skeptical that what a lot of these shops are selling is all zheng yan material even if they claim it is, but the teas do have a characteristic taste that's hard to describe. Sometimes I feel the roast is a little too high, but it does make for a pleasant tasting tea much of the time.
I wouldn't consider Tim's 2008 one to be the same kind of "high-fire", and to the best of my knowledge, it wasn't roasted in HK, though of course he would know better. Tea Gallery's recent stuff (not counting the Tie Luo Han you're talking about), even the more roasted stuff, tends to be more balanced too, at least from the stuff I've tried.
I could be wrong, but I think a lot of what you're tasting in some of these teas is the fact that they have a higher degree of oxidation. If the tea isn't so roasted to hell that you can't see the color of the leaf, you can tell by how much red the tea leaf has, especially on the edge; you can also get some clues by the taste, and by the color of the brewed tea.
Also, everyone's idea of "high-fire" or "traditional" is different. The more tea I drink, the more I seek balance in the teas I drink. That's not to say that I don't enjoy a super high-fire tea, because I do, but I do find myself gravitating towards teas that aren't all roast and no green.