Of course the dynamic range in productivity of engineers is much higher but, similarly, the market isn't that competitive and you don't have to pay that much more.
When I worked at a chip startup, we paid ~20% better than public companies (if you wrote off our options). Our 40 person team taped out a CPU in 1 year. Our most famous startup competitor, Transmeta, had ~300 people and took 4 years to tape out, a 30x difference in productivity and why we survived and they lost $1B and went under.