I have not found other sources to confirm what I said in my previous post about Windows Vista users, so I'm skeptical of what that article seems to be saying about Windows Vista. It might simply not be correct.
It says: "Upgrading to Windows 10 will require Windows Vista users to do what’s called a fresh install." If by "upgrade" you mean an in-place install of the new OS that leaves your files and programs intact, then Vista users can't do this, free or paid-for.
Users running Windows 7 Service Pack 1 or Windows 8.1 S14 (that's the “Windows 8.1 Update” from last April), will be be able to get Windows 10 straight from the Control Panel's Windows Update utility. They won't have to make an installation disk, and their files and programs will remain intact. Cost: zero
Users running an older version of Windows 7, Windows 8, or Windows 8.1 can also keep their files and programsi but will have to download an ISO and create an installation disk. Still free.
Users running Windows Vista and Windows XP (with compatible hardware) will have to pay for an upgrade to Windows 10, and this will require a clean install that erases all programs and files.