Think of it this way - do you think it'd be healthy for a person to play World of Warcraft for 80 hours a week? What if they were having fun and it felt like they were only playing 30 hours a week? Just because you're building a startup instead of playing WoW doesn't mean it's any less unhealthy.

What I'm suggesting is that working 80 hours per week is by its very nature harmful to you, your coworkers, and the company, regardless of whether it sout of interested for the things you're doing. It leads to scope creep, burnout, and other unhealthy outcomes. Everything should be done in moderation, including (especially?) work. I can foresee a situation where you or somebody on your team will ignore the obvious signs of burnout and power through until its too late.

If you feel like you need to work that much I would suggest you re-evaluate your scope or find more coworkers. Look to other companies who have built fantastic products without sacrificing a good work/life balance (37 Signals comes to mind).