Boiling it down to the core point, "the Bolt will let GM sell more swanky Silverado pickups at much fatter margins without paying penalties or buying credits from competitors".

It's important to know that fuel mileage regulations are calculated on a fleet basis, not per model. So manufacturers are actually trading off optimizations across their entire product line. The Bolt is just an iteration on the existing strategy of using cheap small cars to offset the emissions from larger (higher margin) trucks.