Also one point can alter the position of ALL points, for example in a ADSR envelope if you move the attack point all others should follow it, that is keep the same distance from the attack point, but some envelopes need for the points to stay in place.
Can you give an example? I can think of envelopes that control equalizers, like in the cubase mixer. But that would be a different type of envelope I think, because the x-axis is a value line (frequency), not a timeline, and so all points would be valid on the entire range (axis that is..).