It's always been that way, sort of. The black line at the bottom has alway been there in order to make it so your HUD elements at the bottom have somewhere to go that is not in the way of gameplay. In other words, suppose there was a door at the bottom left of the screen and you needed to get there; it could be directly covered by the HUD if we didn't let the view go lower by that amount.
That has alway been there. However, our practice of cropping the outdoor hunks so that they don't have a lot of useless underground area (if it's literally just dirt, we cut it off) is relatively new. That makes it so that in many areas your view gets naturally pushed up and off center from your character on the y axis, showing you more sky when to show ground would be pointless. A player request in that case, and I thought it was a good idea.