Brake pads usually last an average of 15,000-20,000 miles.
Not quite sure where you got that figure from...
Our fiesta has done 32k miles and the brakes still have plenty of life in them. If i remember correctly, at its 25k service, the brakes had about 50% left in them.
My mum had a Volvo S40 and that had 55k miles from new on it when she sold it and its brakes didn't need to be replaced.