My point is that the other side could be argued just as easily. The outer 80 m spans of the Kap Shui Mun would have to be much shorter if they were not receiving support from the stays.
I am only familiar with a handful of the bridges on this list of the 117 longest and was able to point out an example where there is subjectivity in total cable-supported length. I have no idea how many others on the list might have be debatable and therefore question why it is as simple as you say.
This is the same reason why the article List of bridges by length has a big disclaimer at the top that basically says, "Hey, we are not really sure of these numbers. We don't know where the measurement starts; we don't know where it ends. In fact, some of these numbers are just plain guesses."
It sounds to me that you are proposing a column on this list that will require the same disclaimer once future editors add or edit information. -