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).
We, of course, hope that we will not have to work 80 hours every week down forever - but at an early stage we can't help ourselves. The extreme motivation, energy and drive in the team keeps us running.