All of the electrical outlets in our 1959 home are mounted horizontal. They are mounted in a piece of 1" X 6" that is nailed between the studs. The neutral prong is up sometimes but often not. All outlets are have a ground prong but most are not connected as the 12-2 romex has no ground with.
The owner/builder was a carpenter and 1/2" sheet rock was used to finish the walls. For me the best thing is all wiring heads to the basement, making rework very easy. In other words, where we today daisy chain from outlet to outlet through the stud bays, this house has each outlet heading down to the basement to a junction box.
So, the question is why horizontal?