I don't see the issue - simple law of business, supply and demand. They are free to charge what they want, and if they make an acceptable profit at x-amount, they will continue to charge that much.
Maybe the expensive petrol stations simply don't want to be dealing with peasents, maybe they attract a higher class of people who just don't give a damn about prices, personally id probably avoid a petrol station charging 10p a litre higher than the norm for a particular area, but thats just personal preference.
Down by my dads, (Herefordshire countryside) the petrol is always 15p per litre higher than around here, sometimes even more, we don't realise how lucky we have it in all honest, we have some of the cheapest fuel prices in the country within Merseyside. And at the end of the day, its only fuel, and its only money.