Designers have the ability to use so many options to make a headline or any amount of text more prominent that underlining should be one of the last options we consider. There is a difference between using a line as a divider but when it is as an underline you are digressing to the days of typewriters when they didn’t have the option of so many design options for adding more emphasis to type. In this example the headline is already larger than the type size used in the list so the underline wasn’t necessary.