> I'm 100% committed to working for the man
So - no wife, kids, friends? Everyone has interests and activities - even passions - outside of work, and for some people that can be a nascent startup, simply a fun side project, or maybe some open source code that's great for learning or honing skills on. What you do in your own time is your own business.
> doing a startup "project" while working for the man would seem inefficient to me
The problem is this: startups at the 'idea' or 'a bit of code thrown together' stage can't really earn you a living, so you need to find a way to fill that gap. You can work on the side, a bit at a time, ala patio11. You can get investment money, so that you can commit full time, which is great, but is something outside your control. You can also save up some money and take the plunge, but that's not always a possibility either.
In short, different things work for different people.