Who is this Gartner research group? Ok, I do know who they are but it feels like whenever I read one of these "blasts from the past" articles they have an analyst in there making some statement that is way off mixed with terribly inaccurate predictions.
If Apple hadn't made iTunes available for Windows machines, there's a very likely possibility that the iPod wouldn't have taken off the way it did.
iTunes for Windows came out in October 2003, and then the iPod Mini was released in January 2004. By even that February I recall the iPod Mini being a grand slam seller. The combination of Windows availability and the Mini being an option at a lower price point were when the stars seemed to have aligned for the iPod.
I think e big hurdle for Windows users back then was the FireWire requirement. Not many PCs shipped with FireWire.
Probably 70% of their business is producing analysis that allows people in the government or large companies to justify buying things. Google "Magic Quadrant", which is a gartner thing that lets lazy IT executives pick a list of vendors from a checklist.
Like anyone who tries to predict the future, Gartner gets things wrong all of the time -- they base most of their conclusions on client interviews and vendor dog and pony shows. That said, they do collect good information and you get alot of good insight from talking to the analysts.