In the aftermath of violent storms that knocked out power to millions from the Midwest to the Mid-Atlantic , sweltering residents and elected officials are demanding to know why it's taking so long to restring power lines and why they're not more resilient in the first place.

The answer, it turns out, is complicated: Above-ground lines are vulnerable to lashing winds and falling trees, but relocating them underground involves huge costs — as much as $15 million per mile of buried line — and that gets passed onto consumers.

With memories of other extended outages fresh in the minds of many of the 1.07 million customers who still lacked electricity late Tuesday, some question whether the delivery of power is more precarious than it used to be. The storms that began Friday knocked out power to 3 million and have been responsible for the deaths of 24 people in seven states and the District of Columbia, including a utility contractor who fell to his death Monday in Garrett County, Md.