You are talking about polyphasic sleep, which when you train and skill is a great tool to sleep less, but I think these guys are not talking about that, they talk about being "la tête dans le guidon" as we say in France => head in the handlebar litteraly, or "sous l'eau" => underwater. It is a myth. Startups are all about creativity. If you don't sleep enough, you are not creative. PERIOD.