Gartner is, as usual, smoking crack.
Any business with an IT department worth a damn will require any new software, be it an individual application or the whole operating system, to be validated by an exhaustive battery of compatability & stability tests before being implemented. That testing has, can, and may always take YEARS to complete, and trying to rush it just ends in disaster. So for a business to go from Win7 to Win9 will require said testing to make sure the OS will be up to the task, to determine what, if any, hardware upgrades will be required to run it effectively, and that all the software they currently rely upon will accurately, continuously, reliably, stabily run upon it. And if that takes so long that MS EOL's the thing before said testing is complete, the company has to start all over again on the newly released OS, at which point the testing cycle starts all over again.
So if a company takes ~5 years to validate & certify the OS to do what they need & run what they need it to run, only to have MS EOL the sucker before they can deploy it, that means the company won't bother to make the transition because they're going to have to start that testing cycle all over again with the next release. So a Win7 to Win9 jump would only be financially viable IF and ONLY if MS agrees not to EOL the damned thing before people get to validate, certify, and deploy it in the first place.
It's kind of difficult to justify all the costs inherent in that task, only to try & justify them all over again before you're finished.
TL;DR: We had over a decade of XP to work out all the bugs, get it working, and make sure all our stuff worked on it like we needed it to. MS needs to make sure we'll have that same kind of time on Win7 and beyond, else everyone will go broke trying to keep up with MS' artificial upgrade pace.