It sounds like you are referring to the guidelines for how long the measure should be for for optimal legibility. What I'm saying is that aside from legibility,

It sounds like you are referring to the guidelines for how long the measure should be for for optimal legibility. What I'm saying is that aside from legibility, the length of the measure also influences user behavior - a shorter measure nudges users to write shorter comments. Comment replies are indented by 20px per level, making the problem that much worse. They could easily increase the measure and still stay within typographic guidelines.