Earlier quoted context omitted.
I see what you're saying and I agree it would be great to be simpler. My perspective is that the complexity is actually in the flexibility in CSS and the number of options provided to you. I'm not sure how I'd make it simpler without removing some of the control.
honest question, but what would the problem be with having "margin: auto" work vertically as it does horizontally? EDIT: I mean, what freedom would have been lost when it was designed to work like this, not talking of changing it now.
What would you do with this case then?
.outer {height: 1200px; width: 800px;}
.inner {margin: auto;}
This is centered vertically
But where should this go?