I managed to get some time from our head of UX who explained that the positioning logic was designed with respect to the left-hand panel of SSMS, i.e. the database browser. The logic being that a commit should be adjacent to this panel since it was a local action, whereas an update was more of a remote action. So there's no implication of importance but only physical location. He also said we may review the way source control looks and feels so we are keen on your feedback.