I think 20%-25% might be over estimating it a bit. 9% XP, 1% Vista, and sure 50% Windows 7, but if they are connected to the internet it should be SP1. But it's hard to say, especially in the test system fields, where older machines are more common than consumer devices, and being isolated from the internet is more common than a consumer PC. Still I consider myself up on the latest updates of NI and LabVIEW and this was the first I'd heard about it. "Not being clear and upfront" is an understatement.
BTW that's a neat site.