Microsoft made the upgrade from Windows 7 to 8 Pro $40 for a year after release. That's a pretty good deal, considering licensing costs to that point. Windows 8 ran better on older equipment than Vista or 7 ever did, so in terms of old equipment, if you were running anything after XP, 8 is the fastest, most efficient, mass market OS since XP that Microsoft has released. Touch is a red herring as the performance was worth upgrading for. Windows 7 supported touch also, as did previous Windows releases, but nobody ever touted that as a reason they chose not to upgrade.
10 is free for more than one reason. It's hardly a finished product. I highly suspect it would fail worse than 8 in the upgrade market, and in the end, it's really all about the money that is to be made from Windows as a service, not a product. If Microsoft had been willing to add the old start menu to 8, Windows 10 wouldn't even need to exist with it's myriad of issues.
Windows 10 is a very restrictive version of Windows, and also collects the most personal data, probably the worst in that regard that I can think of, not including starter editions of course. Since folks decided to forgo judging 8 on it's technical merit, but valued it on it's UI alone with a form over function mentality, they are now stuck ushering in a new level of feature and performance loss and thinking they are getting a great upgrade.
How about Windows 10's universal calculator app? Great upgrade from 7 and 8, right? So intent on pushing their universal framework for apps, they throw away software that is actually faster and more usable for an app that needs a splash screen during startup. Great business model. Convince everybody you've lost your direction.
How about shoehorning 75% of Control Panel's functionality into a universal app as well? It's all fun and games until you realize, you can't have two separate settings pages open at the same time. Since they all run through the same app, every time you want to look at another settings page, you have to leave where you're currently at. This is a bit of a problem if you haven't memorized the locations of all the settings yet. It's confusing for no apparently good reason. With Control Panel, if you were drilled down into a particular setting, opening a new Control Panel really opened a new Control Panel, not just reused some old settings app window.
Another favorite of the interface changes is the left side swipe gesture. In Windows 8, it made sense in that, if you had other apps open, it switched between them or brought up the app switcher. If you had no other apps running, it did nothing, like it should. In 10, a left hand swipe brings up the Task Switcher, whether you've got any tasks to switch to or not, requiring the extra step of undoing it, if it was an accidental gesture, or better yet, if what you were trying to do was move cards on a left hand column in Windows 10 Solitaire. Don't worry, the Solitaire folks fixed the issue by making the gestures in apps into two-part maneuvers. Completing the transition from the mediocre touch interface Windows 10 shipped with to something even less usable. Yep, totally love trying to hit the tiny X in the top right corner of universal apps with my finger after first pulling down the bar. If you miss, no problem, you can pull the bar down and try again.