You think startups are any different? Unless you are one of the very first employees in a startup that is massively successful, you're not going to benefit financially compared to a job at BigCorp. In fact, the loss of higher salary, bonuses and benefits mean that startup employees are often working longer and getting less in return.
It's time to get rid of the culture where you have to stay in the office as long as the founder does- his incentives are totally different. A 40 hour week sounds great to me, but it requires a cultural change, not a legal one.