Kidderminster - Marylebone trains are travelling in the down direction between Kidderminster and Stourbridge (the mileage is towards Paddington via Worcester in that part of the world) which probably highlights two things, that the "up" and "down" is a rule of thumb, mostly its geared towards London, but the XC route uses Derby for long stretches and (I think) most of Scotland uses Edinburgh. More importantly, the lines have names so the people on the ground, drivers, guards, p-way, can be specific with what they mean when they are talking to the signaller. It's not about having a system which fits the whole country perfectly, it's about being able to identify things locally.