What I expected:
I expected the Wither I just created to face in my cardinal direction, or at the very least, for the Wither's orientation to correspond to its totem's orientation.
What actually happened:
Withers always spawn facing South.
How to reproduce:
Create Withers, and watch which direction they face initially.
It is really more an aesthetic thing than anything, I'm sure. Especially for totems where the arms point North-South, where you see the Whither emerge 'sideways'. It seems to detract from the idea that they emerged 'from' that Soul Sand structure.
Every utility mob spawns facing South, every mobs spawned from mob eggs are facing south.