CEO work/responsibility doesn't really scale up with company size, though. Sure, they're "responsible" for more people; but it's really the people that work for them that are responsible, and the people that work for them. Scaling up the size of a company generally adds more layers; it doesn't add more work for any individual at a layer.

Admittedly, that doesn't really hold true for the initial "small company to large company" growth, but that's not really what we're talking about; and _that_ hasn't really changed at all in a long time.