Id argue Microsofts strong suit here is making themselves
look competitive. During the web server wars Apache reigned supreme, until the numbers shifted in favour of IIS which overtook Apache for a time. Was this a better product Apache was fending off? no. Microsoft had paid hosting providers to park web domains and registrations on IIS servers so Netcraft would finger them as #1.
now we have Azure and its the same thing all over again. Azure Cloud has lots of tenancy, but these numbers I suspect are bogus. Azure runs Office 365, Exchange, Bing, and Xbox Live assets as well, and these are all "tenants." MS also bundles discounts for business critical things like desktop and server licenses into accepting Azure credits, so its likely many of these tenants are on paper only.