It's not particularly unusual for it to be difficult to downgrade OS due to changes in technology, the issue is just more prominent of the mostly unfounded consumer dislike of windows 8 resulting in a larger number of downgrades. The introduction of secure boot and uefi 'breaking' windows 7 isn't far removed from the introduction of SATA controllers 'breaking' windows 2000 or linux 2.4. If anyone is trying to resist downgrades, it's OEMs and hardware makers (who are then responsible for drivers, support, etc.), not Microsoft themselves.