The NYT article was interesting and, as OakLeaf says, alarmist. I think that, regardless of the instructor's skill, many people tend push themselves into situations they should not be in. "No pain, no gain" is a deeply rooted belief in the US (no equivalent phrase in Spanish, for example) and there is nothing unique to yoga practitioners in that respect. People might be making a pose more extreme to "feel the stretch," ignoring pain when they run, etc.