That's pretty much all it is, i hesitate to call anything after XP an upgrade. The only reason i got 7 was the higher ram limit, along with slowly phasing out useful features and making the gui completely alien, we also have the ever growing list of games which don't work anymore, or at least not without hard work from fans... some games don't have those brilliant communities dedicated to keeping them functional.
I know Vista made some games unplayable, i know for sure that since 7 getting Red Alert 1 and 2 installed and working is now a hassle, i couldn't get Brothers in Arms: Earned in Blood working at all, 8 made more recent games unplayable without patches, most recent one i'm aware of was The Sims 4.
... It's been getting worse.

You want advancements in OS security and performance to come to a screeching halt because some games and apps built for antiquated, poorer performing OS's don't work on newer ones.

It's the business model that stops Microsoft providing security updates to its older releases, if a new OS is required to keep up with security then it's not a well known fact, hackers tend to dismantle new OS's before they're even out.
Performance is hard to see because they added Aero and Metro which both require CPU cycles and memory (minor, unless you love apps), i'm sure current games run roughly the same on 7 as on 8, otherwise we'd have all flocked to it for the performance gain.
DirectX 12 aims to bring vast improvements, could they have built it for use on 7 as well? Probably.

All of this is missing the point though, i love video games, PC's are massively important in the history of video games, every game ever made should continue to work if only for historical purposes, in 30 years time if you want to make a video to educate people about Skyrim i hope you can.

Aero isn't in Windows 8 and Metro really doesn't have any more of an impact on performance than the Crayola-fied UI of XP. If you're talking specifically about Metro apps, there is some performance hit there but those are all nearly 100% optional for usage, and almost all animation style stuff can be disabled as you could for years now in Windows. As far as performance is concerned in games, there is a steady stream of proof that 8.x performance is better than 7.




Etc.

It's not sweeping performance gains across all games and all hardware configurations, but they are there. Even more, the performance increases aren't just for games, but for normal OS and app usage as well.

And yes, they probably could have built DirectX 12 for Win7 and maybe for even older OS's. But it doesn't make sense for them to do that. They want as many people as they can on the new operating systems so that they can stop supporting older OS's like they did with XP. It would speed up updates significantly if they don't have to allocate resources to older software support. And the fact that people make malicious releases for new OS's is kind of a moot point. They're going to do that for all OS's regardless and are actually more going to target older and unsupported OS's like XP because they know security holes won't be officially patched like they will be on newer ones.

But yes... PC gaming is awesome. Console gaming is just as awesome.

Indeed, and ironically it's PC's keeping console history alive through emulation :P (let it be known i'm all for re-releases, keep games easy to use for all).
It's free nature has me slightly worried, what other business strategies will MS use for earning money through Windows 10? But in any case, here's hoping MS can build a chair we can all sit in comfortably.