"Another oddity: Squarespace and Wix, both of which advertise heavily to small business, have 0.9 and 0.5 per cent share among CMS-users respectively."
Not that odd. If you're a non-techie plumber looking to set up a simple website for your business, Wix is probably a reasonable solution (never used it myself, so can't say). But that website is unlikely to make the top 10 million sites on the web, so won't be counted in the survey.