It only depends heavily on the up vote if you depend on the up vote. Sometimes it's nice just to formulate thoughts in writing. If others see it, great. If not, no big deal.
I think they explicitly said the opposite. That the writing is their reward, and comments are always visible to the author. Visibility to other humans is incidental, or at least a secondary concern.
They explicitly said, "If others see it, great. If not, no big deal."
So I agree they get some reward from the writing. (Like all writers do, and like we can all do just as well with a journal.) But the part I just quoted is clearly part of the reward function, and just as clearly the total reward increases with others seeing it. Which on HN is controlled by upvotes.
They also said "Sometimes it's nice just to formulate thoughts in writing". "Just" implies sufficient reward. Visibility is a part of the reward function, but it is not dependent on it.
Fair question. I think 'depends' has different connotations if you are talking about a binary outcome or function.
If I were to say something like "life depends on water", the connotation is that water is a necessary condition. You wouldn't use depends if the dependency is situational e.g. "life depends on shoes". Shoes might be the difference between life and death in some situations, but irrelevant in others.
That is to say, if a factor is a poor predictor of the outcome, but perhaps correlated, depends seems misleading.