How so? I suspect you might be thinking that the comment could be saying to look at that difference in preference to (or to heavily influence) Stop depths?
I assumed that the range (30-40) would be something that aligned with Stop depths. Especially given the perceived calibre of the person making the comment.
I mean simply this: My expectation would be that an untrained person would not be able to explain what the 30-40 number means and why you want it to be in the 30-40 range, instead of, say, the 70-80 range.
Which means that you then potentially have a person making decisions about their ascent based on something they don't understand and have no real training on. Generally speaking, I am an advocate for people doing things the way they were trained. And, in particular, NOT for doing things based on an off-the-cuff generalization that they were told but don't REALLY understand all the Whys and Wherefores behind it.
I'm not saying you in particular are an issue with incorporating that advice into your diving. That is why I said "an untrained person COULD get in trouble."