These companies are buying gold as they think the price of gold, in general, will be going up. They're not doing you any favours, they want to make money.
Why are they buying Gold? In a nutshell, gold maintains and even increases in value in periods if inflation.
How could there possibly be inflation when we're in such a mess? Because the economy is awash with liquidity that the Bank of England has printed out of thin air, ie quantative easing. When Britain finally comes out of recession,the banks become bullish and start lending out this printed money to the real economy this extra £80 billion swishing about will bring inflation.