...which it increasingly is, as more and more 3rd-party services provide client-side javascript SDKs (head over to a billion young startup sites and see if they don't have a 'mixpanel' object loaded), as well as the telltale signs in markup and CSS. As well as API keys for various services hanging around in their client-side code, which is a little mind-boggling.

Anyway pretty brilliant idea to keep running stats on this stuff. $$$$$

I'd be curious to hear of a couple examples of software large companies buy that is visible from their websites.

Analytics, highcharts, status page, blogging tools, ticketing software, project management software, crm etc, etc... The article gives more than a couple of examples.

Anything that offers third party js or offers hosted solutions is going to be pretty easy to find.

Yeah I was wondering that too.

Maybe it's mainly for competitors to apache ...