"It's as if MS are back where Apple were in the late 90's...They know the OS needs an overhaul, but are bodging the overhaul as well instead of re-architecturing the OS from the ground up."
What a pointless argument. Apple were a nobody with a nothing footprint - particularly in the business world. The effect of "re-architecturing" <shudder> was minimal because hardly anyone was (is) using it. The loss of backwards compatibility only affected a tiny number of people and they were mainly home users.
For MS to re-build Windows from the ground up and lose backwards compatibility would destroy the company. The reason people upgrade their Windows OS is because they perceive (right or wrongly) that they are gaining extra benefits/features whilst maintaining the set of applications that they already have. In other words, their past investment is not wiped out.
I know this is a hard concept to grasp for your average mac user but BUSINESSES invest millions in software for windows. They are not going to write that off overnight because MS want to re-build windows from the ground up for architectural reasons. The MS CEO who makes that call will get laughed at, then sacked.