I think the ability to earn money, however you do it, is a good measure of the lower limit of someone's intelligence because at the end of the day there is only a finite amount of money in this country as defined by the Bank of England1 and therefore we are all in indirect competition for it. This is achieved by value being placed on goods and/or services and that being represented by an income.
So with the footballer and porn star arguments, it just shows what strange things humans place value in! Art I believe has its own value, but not one that many modern-day capitalists have much time for.
1 - On a side note, how do they govern and introduce new money into the economy? I realise that introducing more money without controls makes inflation spiral and devalues the currency against foreign currencies, but where does it enter the economy? With the government? UPDATE: This seems to give a good idea of how it works (and the effects of hyper-inflation) - through loans to businesses.