Actually, probably not. Sometimes I still make an app that doesn't do too well. I guess this is the downside. To get started you have to be prepared to make several apps (maybe even up to 10) to be reasonably sure you'll start getting a good income.

But when you do get one, it can generate revenue for a long time coming.

I think with some good market research you could probably be more sure though. And also going into partnership with somebody lowers the risk as you can churn out more apps then share the profits when you do get a successful one. Personally I have not had much luck with the Apple app stores because of their crowded/discovery issues etc, but I also have not put much effort into them due to their horrible restrictions (the sandbox is a killer with the way they've implemented it, and a lot of my software needs admin privs to run)