Win 10 is a free update. Microsoft service packs and updates are also free, Normally, new OS versions are not.
They will be, MS is going to be forced to make OS upgrades free for the end user, or they will lose even more market share... Reality is, Apple’s decision to give away OSX ended up SAVING the company Millions of dollars over selling it, at this point, like it or not, the price point for an OS to the end user is free, MS will eventually realize this, if they haven’t already, they can charge OEM’s and corporations $$ if they can make them pay, but the days of the end individual consumer buying OS’s are done....
Of course MS generally takes 5 years to recognize where things have gone trying desperately to protect turf that is no longer viable, and finally capitulates, so they might try to hold on for a few more years but reality is, 10 being free likely is not a one off, but just them coming to terms with reality, that and the fact they need the bastard hell boy that is 8.x GONE from the consumer consciousness as quickly and fully as possible.