Consumers don't generally buy PCs because a new OS is out. They buy a new computer because they want or need one.
It isn't like the introduction of a new technology (eg. when iPads appeared). It isn't an additional device.
Businesses have a fixed rollout time usually, so new OS vs old OS isn't a discussion that's made for existing kit usually. They usually just replace PCs at the end of their planned lives, and prior to that the new OS is tested etc... The problem they have faced though, is compatibility - existing programs ceasing to work in the new version, so that caused them to hold back on the entire project.
If Windows 10 can run everything that Windows 7 and Windows 8/8.1 can, then there is less of a hurdle to overcome to encourage an upgrade.
We won't be upgrading to Windows 10 in our school until the next replacement cycle anyway, as there's simply no need to disturb our stable network!