I'll admit to not reading the entire article here but I think that mostly people mistake posture issues for lack of exercise / being sedentary in general. If you work out a minimal amount and build some core strength / back muscles etc then you'll find that your posture naturally corrects itself whilst walking, that sitting in a chair for extended periods isn't as rough, etc.
Recently I decided to find a new hobby and started playing the violin. It was a wakeup call that after just a half hour standing playing the violin with my instructor that my back would basically seize up. It was quite embarrassing! Good thing is I got used to it pretty quick, and thanks to violin practice I stand much more than I used to (and plus I added more back and stretching exercises to my workout). As you say, it really takes a minimal amount to improve your strength.