That's the typical American publishing style, which makes sense, as you are American (er, I think. I apologise if I am mistaken).

My mum also inserts two spaces after a full stop. Do you know why you do that? If I recall correctly (and I may well be very wrong), the 'two spaces after a full stop' rule originated from use of the typewriter, because one space wasn't very clear when all the letters were the same width. Did you ever use a typewriter? Were you just taught to insert two spaces?