It is unlikely that more than 1 or 2 people in a small company will have any major health issues, so if you are signing up 20 people your overall risk is lower (in your example a $10,000 per person cost).
Combined with different feelings toward risk, usually health insurance is a win win. The annoying thing about the recent "reforms" is it mandates preventative care be covered, eliminating the ability to get pure "oh crap" coverage.