Some networks prefer a uniform numbering scheme. /112 allows for reasonable addressing needs on a circuit. In addition, while Ethernet is often used in a point-to-point access circuit, such layouts may change and renumbering would be annoying.
Finally, having chunks 4-7 define the circuit and chunk 8 provide the circuit addressing makes it more human readable and is prone to less mistakes by those who suck at math.
Jack
I actually see that as a pretty good compromise. You could have all of your point-to-points at a pop in the same /64, you can give them all ::1 and ::2 addressing, and the addressing scheme supports both point-to-point and point-to-multipoint topologies. A customer with multiple locations in a region could run a circuit from each location and they could possibly all be in the same /112. If they want to multihome to you, they run similar links to a different pop in a different /112 in a different /64 that is part of that pop's /48. And the numbering is consistent at the user end. The ::2 site or ::3 site would be the ::2 site or ::3 from both pops with a different prefix. Seems reasonable to me.