Earlier this year, Apple released its list of top iPhone apps at the one billion download mark. Downloads just hit two billion, making Apple's "All-Time" Top Apps label even sillier than it was at the time -- but that aside, it's a very interesting list and there are a lot of good lessons to be learned from it. We know that developers of some top apps have earned a lot. Some have probably earned much more. It's difficult to estimate income even if the number of downloads is known, because app pr
less...