Re: Why free?
"What Microsoft want is for everyone to take their five year old PCs and laptops, upgrade to Win10 ... and then find that the drivers are a problem, the memory needs increasing, the processor isn't up to it etc"
If so they may be disappointed. I ran the preview on an early Atom Mini-ITX board which is pretty basic H/W. The only driver issue was for an HP printer which I solved by downloading the 8.1 version from HP. As a matter of interest it would run Lotus Smartsuite (installed in backward compatibility mode) which I installed as a prerequisite for one of the old Office 97 competitive upgrade installs, also running in compatibility mode.
Will it tempt me to migrate back from Linux? No. Migration from Linux will be to BSD.