The first problem is actually shipping something that customers can buy. I'll skip over this because both Nathan and Amy have certainly been able to do that. So the next step, the 'white whale' project is the infamous second project.
The advice out there suggests either:
1) Outsource Development (it certainly helps if you're a developer)
or
2) Learn it the hard way and do everything yourself
Rob Walling has certainly had fantastic success himself - all by outsourcing. In fact, if I remember correctly, Rob struggled to successfully launch countless products before he chose a different route. Rob chose to purchase existing businesses (HitTail, Beach Towels etc.) and then started marketing them . I don't believe he had any success before that.
Amy Hoy has had great success with building everything herself - Freckle being a great example. However, Amy has also failed with Charm: "It ended up with me spending 2 years and $200k on something I had to shut down."
It seems like it's not just as simple as choosing either option 1 or option 2. There are examples and counter-examples to both options.