About weight, count me in as someone who didn't realise you could be at a healthy weight and still have countable ribs!

It's called a "range" for a reason though. Bone structure, metabolism, etc, mean that two people of same height might be at opposite ends of that healthy range.
This being said, it also means that people can be at opposite ends of the heathy range and BOTH be unhealthy, because the thinner one of the two should be on the upper part of it and the heavier one should be on the lower part of it rather than the opposite.

To take the example of 66 to 88 kilograms, obviously if someone should be one and they're the other one, it can be a problem.

Exercise is indeed the best way to regulate your weight to what it should be (meaning you'll lose if you're overweight and gain if you're underweight) provided you eat healthy too of course. (Eat after exercising so that it can rebuild the muscles you've just been tearing, and make sure to get a bunch of protein in that meal).

I think it's a bit sad that nowadays people get scared when they're barely heavy, and don't worry about being too thin, as it can be a problem too. I hear the "healthy" BMI range has even been changed from 20-25 to 18-25 because too many people were under it. That seems silly.
18-20 used to be "underweight", the equivalent of the "overweight", and under 18 was "severely underweight" or the equivalent of obese but the other way around (as in it becomes medically bad for you).
There is no reason why 18-20 would suddenly be healthier than it used to be, but I heard that since models often fell into that range, it got changed so people couldn't say models weren't healthy. Pretty silly altogether.

The weird thing is that wikipedia still has the old numbers in the description:

a BMI of 20 to 25 may indicate optimal weight; a BMI lower than 20 suggests the person is underweight while a number above 25 may indicate the person is overweight; a person may have a BMI below 20 due to disease; a number above 30 suggests the person is obese (over 40, morbidly obese).
But then their chart shows up to 18.5 as normal. So they're using both ways at the same time. No wonder people get confused.

(BMI is obviously not the most accurate thing ever, but it's a common way to get a general idea when you're sedentary, which is why it's what I'm talking about here).

Since we're on the LGBT thread, I wonder if the weights compare with the general population, or if due to bullying, non acceptance, etc, there are more eating disorders for instance.