The standartd requirement for stair/step dimensions are 7" rise, 9" going. This means that the thread size is 7" high and 9" long. The usual room hight is 7'6" high resulting in 13 steps. Actually the step hight is 6.92" high.
The house that I was brought up in was built in the early sixties and had 14 stairs in one straight run, I remember being most confused/disturbed when I discovered that other numbers of stairs existed. My current house (1920's) has 14 as well.
Don't know about old stairs, but I used to be a civil engineer (in the 80's/90's) and one of my jobs was checking calculations and drawings etc for Building Regulations submisson for the local council. One of the 'rules' is that you are only allowed to have 13 steps in a flight. Any more and it must be 'broken' by a half landing or something, although I don't know the reason this rule was instigated.
Thank you glenis, you've just made me get up and count them :-)
Perhaps it's because our house was built around 1900 but the stairs add up to 16..straight up no bends. A long way to fall - I know as I've tumbled twice!