One of our apps, Contact Clean Pro, jumped up to nearly the top 50 in Productivity.
The day it jumped up wasn't a particularly good day for it, selling 4 copies. The recent best was a couple weeks ago when it sold 13(!), about the time it was at very bottom of the top 200 graph above.
So for iPhone Productivity apps, any app that is out of the top 200 is selling single digit copies a day at best. So of the thousands and thousands of productivity apps, most are making virtually nothing. With a very large percent making absolutely nothing.
But the lucky 10 or so at the top are likely selling hundreds or thousands of copies a day.