I'm glad that you've had a good experience with Windows 10, but this is still a big deal. There are a lot of reasons this is different from Chrome and Firefox updating, or even from Microsoft automatically delivering updates to Windows 10.
Windows 10 is not just an update: it's a completely separate operating system, illustrated by the fact that you have to accept a separate TOS. And while the upgrade may be free, the OS is not. I have never heard of an involuntary OS upgrade, and it's ridiculous that Microsoft is trying to impose one now. No rational user of Windows 7 would suddenly expect to be force-upgraded to Windows 10.
Yes, Chrome and Firefox will force you to update when you restart your browser. Yet although they might nag you, they won't forcibly restart your browser for you. This is what Microsoft is doing to users' computers: the upgrade might take hours and download gigabytes of data, even if the user never asked for it. This is effectively holding computers hostage. If a computer is being used in a safety-critical situation, even if it shouldn't be, that's a recipe for disaster.
Finally, Windows 10 has downsides that Windows 7 doesn't. First, the upgrade itself might not succeed, as I learned the hard way when the upgrade process simply... stopped. Additionally, depending on your configuration, the upgrade could render your software or hardware unusable: not all hardware may be compatible, even if Microsoft thinks it is. And Windows 10 has more invasive tracking than Windows 7 did, with little or no option for ordinary users to disable it.