Even with new computers, the retailers know this well, such as the following example of the laptops filtered by OS on BT Business Direct's website:
In fact, they have more laptops with Windows 7 Pro than all other other OS's combined.
At work where we use Windows 10, the biggest problem we faced is having to migrate the computers to SSDs as Windows 10 has got incredibly disk intensive, especially when checking for and installing updates, similar to how Windows Vista behaved. It wouldn't surprise me if Microsoft has SSDs on all its PCs and doesn't realise the headache they're causing for anyone still using hard disks for their Windows 10 OS.
So it looks like Microsoft is going to face a repeat of the Windows XP problem, but this time with getting people to upgrade from their trusty Windows 7...