Yeah, but a lot of the people working there will likely have families, and small kids themselves - so taking time off in the summer isn't unusual. And in an organisation as large as this, they wouldn't necessarily bring in temp staff to cover - other people already in the office would likely share the work between them.
And if they don't have kids, they may still be taking time off with family/friends, going to a cabin, camping, fishing, staying by a lake... etc.
I know a lot of people where I work are taking holidays right now (myself included, last weekend!) - though we try and plan it so no more than two people are away at once.