I think you can still have quite a bit of understanding on the overall status of a 30 person company. The CEO has 4-5 direct reports, of which the biggest departments have 10 reports. The CEO can have a pretty good handle on what's going on overall, and people can know their departments damn well.

This stuff definitely starts coming into play at around ~100; then as a department head who's been there since the get-go, you might have 30 reports; on some topics you're an expert who should be directly involved, sometimes not...