I think it's because of that crazy huge storm in 1987 where the BBC told everyone it'd be fine and there was nothing to worry about. Ever since then they've just played it up entirely to avoid getting caught out again.
That's certainly true as far as weather reports go. The moment possible bad weather is on the way they act like Noahs flood is about to begin or that we'll soon be able to host our own London winter olympics, just in case it happens (apparently despite a millennia of it happening, no one expects snow in February).
But whenever it's regular weather they're loath to say if it's rain or shine.
But in terms of psyche, I meant Britain in general. The weather always seems to be the centre of everything, and there's hardly a conversation where it doesn't come up.
Brits just seem to be obsessed about the weather.