Except I think the author would point out that there isn't just _one_ heritability for things like height because height would be much more heritable in environments where everyone has adequate nutrition as opposed to in environments where nutrition was a matter of luck, for instance.
All of this assumes a certain philosophical veiwpoint on what it means to "really exist" which I don't agree with, but which I do recognize as coherent.
It's not even so clear that what many of us would call intelligence is mainly an evolutionary advantage, either.
http://www.marksdailyapple.com/control-gene-expression/
http://www.joebower.org/2010/05/we-inherit-and-we-also-becom...
AFTER EDIT: I'm asked in a reply below what my point was, and it's partly to point out that the term "heritable" means something far, far different from "determined by genes." There are whole books
http://www.amazon.com/Nature-Nurture-Environmental-Influence...
http://www.amazon.com/Genes-Behavior-Nature-Nurture-Interpla...
http://www.amazon.com/Dependent-Gene-Fallacy-Nature-Nurture/...
by professional geneticists, medical doctors, and psychologists patiently refuting the confusion in most popular literature about what "heritability" means, but the main point in this thread is that Shalizi is correct, and many psychologists are wrong, about what heritability figures mean in relation to IQ.
Consider someone like this boy vs his classmates: http://www.sciencentral.com/articles/view.php3?type=article&...
There are of course factors on both sides, but for mental / physical strength I'll happily argue for landing waaaay towards the what-you-do-with-it, not-what-you-have side.
Can you start going to the gym and get stronger than your friends who don't go? No. Out of 10 friends maybe you'll pass 1 or 2 of them in strength, but that's it. That is what I have seen but I'd say it is pretty far from what you suggest.
Presumably your circle of friends consists of people who are already physically active. Even so, I doubt your assessment concerning strength training. Looking at the people around me, I'm guessing fewer than 5% (not 80%) of them are up to 100 pushups [http://www.hundredpushups.com/]
What, you forgot about the massive population of poor the world has, western included? Or how many in the western world eat crap, because it's easier than making things for ourselves? Height is largely determined by what your parents feed you, once you're able to be on your own you're essentially fully grown. I know a decent number of people whose parents were either relatively poor, and they subsisted on mac & cheese frequently, or were largely idiots when it came to food and raising kids. And many of them are noticeably shorter than average. My wife, for instance, is just barely over 5 feet, and her family-then-single-father fell into both categories until he joined the military.
As to the second... I have absolutely no idea where you get that idea from. Maybe everyone around you weight-trains outside of the gym frequently, or you've never done so for an extended period of time? You're absolutely nuts, though.
Muscle mass, depends significantly on how much exercise. Some respond to it differently than others, so some would be more muscular with light exercise while others would be more with heavier. A difference though, yes; if somewhere near the middle, accounting for height / overall body build, a moderate amount of difference, but not a whole lot.
Intelligence, barring physical defects, I don't know. People certainly seem to have specialties, especially if you consider some of the "greats" of history as nigh-savants, but measuring an overall intelligence of a person is a nightmarishly subjective task. Very broad statement: not much of a difference. A lot of specialists are severely lacking in communication skills, a lot of artists in engineering, etc, and those deficiencies would have to be factored in.
At the end of the day, I'd bet we're all pretty darn similar. But I do lean significantly towards the nurture-over-nature side of the argument; do nothing, and you become a blob, regardless of your biology. It happens to animals too. There are, of course, some differences, but you have an incredible amount of control over what you make of you.