By their reasoning, the top paid app in the store sells about 5k copies per day, with the number two app selling about 3k, the number three app about 2.5k, and so on. Vimov estimates that everyone in the top 100 list, when you add them all together, is making about US$304,058 on any given day. The shelf drops off from there -- in the top 1000, developers are making about $372,000, and past that, they're obviously making less.
So, what does this all mean? First, these are obviously estimates; Vimov's app is $0.99, and Weather HD, as they say, peaked in the early frenzy around the iPad's release. They did try to account for that, but even they admit that there's some error involved. Second, things are changing quickly; Apple told us that there were around 500,000 iPads out there last week, but that number is probably much higher a week later. Also, iPad app pricing is still all over the place. Even now, you've got everything from $0.99 to $9.99 in the top 10, which suggests that profits are hard to guess.