There was a time, several years ago, when Google included browser usage stats in its Zeitgeist reports. Probably some time before the Chrome project started, Google stopped including the browser breakdown in those regular reports.
Google is in a pretty special position with the breadth of their usage so their browser breakdown could give the entire industry a much better picture of the Web than what we currently get from analytics firms like Net Applications and StatCounter.
Google search is available in more than 125 languages, is in widespread use in almost every geography on the planet, and Google obviously has the resources to produce solid metrics reporting. So, why don't they? What commercial value is there in keeping that close to their chest?
We really do need something more globally representative than what we have. Google could really help out here.