If I'm not mistaken, Microsoft is a big customer of IDC. While IDC isn't strictly pay-to-play, many of these "independent" analysts essentially make money recommending products produced by their customers. I'd consider it likely that Microsoft's cash is a factor in IDC's coverage.

Also worth noting is that IDC's track record here is pretty bad. From the article you linked:

"IDC predicted that Windows Phone would become the number two smartphone OS in terms of shipments back in March 2011"

Oops.