You hear this question from new(ish) players every once in a while: Why is Preordain banned in Modern, but not Serum Visions? Sure, they are close, but they are not the same. That ordering changes the card quite a bit. Also, they have to draw the line somewhere.
Okay, so if Preordain is stronger than Serum Visions, does this mean you should always scry first, if you have the opportunity to choose? Well, that depends.