The app store is unpredictable.
I've made anywhere from £20 a day to over £500+ on some apps.
If you sit down and actually take the time to make a decent app then there is no reason why you wouldn't make a lot of money.
But a lot of developers just clutter the app store with quick apps, and they don't make too much money (although some do through lucky circumstances).
If you take the time to write a good app, then you will be rewarded.
If you haven't got any coding experience and just expect to make some quick money then it probably wont work out too well...
The money varies day by day, so you cannot depend on the income of the app store to keep it as a full time job.
If you do decide you want to put
hours of hard work into making apps, then good luck, but its not as easy as it seems. Prepare to spend months and months of reading though books, and trying to learn programming concepts that will make you scratch your head until it bleeds!
But if that doesn't put you off, then give it ago. But don't expect to make games like Super Monkey Ball etc... you will need a team of people for that.
Its a lot of hard work, and usually the top games in the app store are written by
teams of developers. Its like the lottery in a way, you hear of people making hundreds of thousands, but thats usually 2% of the 50,000 developers in there.
Sorry this post sounds discouraging,
but if you've read through this and your still willing to give it ago, then I wish you good luck