Collectively, second-quarter earnings of General Motors Corp., Ford Motor Co. and Chrysler Corp. were off 22% from a year earlier - $3.8 billion vs. $4.8 billion. But that masks the underlying story: Ford and Chrysler met or exceeded analysts' expectations, while the $1.2-billion cost of two parts-plant strikes drove GM's profits down 81% from a year ago. GM's bid to prop up market share through aggressive discounting cost a whopping $1,703 per vehicle in the period, up 60% from a year earlier. GM officials say that was offset by lower parts and materials costs. Through mid-July, the strikes slashed GM's production by 227,000 vehicles. Already, the company has warned Wall Street that its July market share in the U.S. was less than 25%.