Clealy not the norm. But it's nice to see some hard numbers. I think if you're in the top 25 apps in any particular category you're probably doing pretty well (exception being some of the lesser visited categories).

That said, I believe it's incredibly difficult to get yourself into a position where you're really making a solid income from your app on the App Store. With so many apps vying for attention you truly need to make your app unique and extremely solid or you risk being forgotten or never seen.

I think the best way to gain momentum is to be the type of app that can be advertised via word of mouth. I don't think I've ever seen Camera+ advertised anywhere (my memory isn't that great so maybe I have seen it) but the word of mouth in various forum posts is incredible. At least at the start this can really help. Once you have some traction and in the top 25 you get the benefit of some Apple advertising via the featured app section (hopefully) and sales take off a bit more for you.

I really think Android will never have this type of sales volume for paid apps. It is pretty incredible what Apple has done with the App Store, and what developers have done with it.