I think a better way to put this is if you want to make GUARANTEED money writing apps... I still think on the whole, its better to release a product yourself than do consulting for someone else.
It's certainly a lot more fun, but if your goal is revenue, particularly as a solo developer, you're going to have to do very well on your own to match what you can easily make as a consultant/employee.
I don't think it has to be either/or. I took about a month off to write my iOS app. While it never made me rich, it still provides a nice income stream that continues today. Now I have my regular job revenue and app sales revenue.
Of course, writing a few apps on the side is also probably the best way to build a portfolio to show new potential clients.