it depends exactly how you measure these things - do they mean average national wage, or gross domestic product per head, or land prices, etc? - , but I suspect you'd find a lot of rural population in places like Spain or France who live on very little (though they may produce their own food) and therefore drag their average national income down. Britain is fairly heavily urbanised. Also, we get freeish health care which Americans for instance don't, free motorways which the French don't, much cheaper world travel than Australians... and so on.