Except when it's not. The cheapest ticket from Three Bridges to Brighton is an Anytime Day Single, at £9.50. The Off-peak one is more expensive at £11.70.
But it gets better! Gatwick Airport is the station before Three Bridges on that route (i.e. further away from Brighton), and yet the cheapest Anytime ticket from there only costs £8. Though to be fair, unlike the Three Bridges ticket this one does restrict me to one train operator... who happen to run four of the six trains each hour on that route... which are the four trains that also call at Three Bridges.
British Rail pricing is weird.