Bill Gates has frugal tastes. Asked to name his luxuries, he lists DVDs, books and takeaway burgers. It is hard, however, to think that any fast-food outlet would get rich on Gates’s custom. During a long list of engagements beginning well before dawn, he consumes nothing but cans of diet cola. For America’s wealthiest citizen, austerity is relative. The retinue of staff and the private jet hint a