This is also an example in the statutory law where a supermajority is required for a decision (five out of seven). I am not aware of any other. Examples of supermajorities of are Constitutional, to approve a treaty by the Senante, to amend the Constitution and in the Senate to invoke cloture to stop a filibuster, and to overturn a veto. I am also aware of supermajorities being needed in some State decisions on budgetting. The United Nations Charter has an instance of a Supermajority being needed.
I believe people should vote on such percentages, and a constrained movement be allowed each year. In high school, we study the Constitution. As each high school student reaches the age to vote, they would have an opportunity to enter for such numbers, what they believe it should be, 70% to overturn a veto or merely 50%. However, the numbers would only be allowed to move a few percent a year. That is we would have political hysteresis. (That limit itself could be voted on the same way.) As individuals died, their vote would be removed and, of course, there would be a procedure to change your preference.