Startups are like going to Hollywood. Your goal might be to become as successful as Clooney, but that's not likely to work out. Still, if you're talented & dedicated, you can make a living in this industry and enjoy it.
I've been working for startups for the past 12 years. I won't be a millionaire even if my current company sells for $.5b - there are preferred stock, dilutions down the road, taxes etc. But I hope to be in startups for the rest of my career, simply because it's fun to create something from scratch, work in a small company with relatively little office politics etc.
It's not fun to sleep under a desk, though, or consistently work 12 hours/day. If your boss expects you to do that, he's a poor manager. If your VC tells you to do it, he's trying to exploit you, as JWZ correctly points out.