stating the obvious

[NightPort]

That would add more stress to the servers to keep you logged in. It would also produce far more errors.

eh, not really. The launcher doesn't necessarily have to do much. Though I understand what you are saying in the traditional sense of launchers. Most games launchers shut down after you hit that good ole play button. But companies could, to a degree, learn from Blizzard here because their Battle.net system only closes when you tell it to.