Because lives can depend on it, and because it might have to be listened to in bad conditions, the shipping forecast has a very strict format. There is no comment by the reader, and no deviation from the usual way of saying things. This gives it a mantra-like quality, which I'm sure is part of its popular appeal, and makes it a rock to cling to in an uncertain world.
In fact, it is a great example of usability, as preached by Nielsen et al.