As you said yourself, Windows is a commercial product - you get what you pay for. Microsoft don't really owe anybody anything beyond what they get paid to do - the only reason they kept XP support for so long is that to do otherwise would be a PR nightmare, all their big customers would be angry and all the regular folks would have machines (even more) full of malware.
The only real complaint I have against Windows' support is that it's update utility, "Windows Update", makes the whole process unnecessarily painful compared to the most Linux package managers.
Just as an aside, Windows Home (which you mentioned the cost of compared to Pro) wouldn't be an option for many businesses because you can't join Home editions of Windows to a Windows domain.
I had a reasonably competent machine, and Vista worked great on it from the day I switched (summer '07, only a few months after it released).
Making the comments others have said about your choice to exclude Vista as a viable option even stronger.
In these 8 years a lot of companies and individuals bought computers and then stayed on XP because (1) Windows upgrades cost money, (2) compatibility issues and (3) fear of upgrades (Microsoft never educated its users to upgrade, quite the contrary, they've made Windows users fear upgrades because of their fuck-ups with Windows ME or Vista).
Windows XP reached end of life on April 8, 2014, with people being stuck on it without a migration path. Nowadays 5 year old desktops and laptops are often good enough and don't need to be replaced. If you had a company with dozens or hundreds of computers, what would you do? Would you pay $120 before taxes for the Home edition or $199 before taxes for Pro, per computer? Would you try to negotiate better terms maybe? Or would you stay on XP because it works? The offer for a 1-year free upgrade for Windows 10 is not valid for XP and Vista.
And yes, Microsoft supported XP for 12 years. That's 4 years after those 8 years in which XP was the only choice. That's hardly an accomplishment.
They still have users on XP. For those users they have an ethical responsibility to provide security fixes, or a cheap migration path (why is the upgrade to Windows 10 not valid for XP?), or the source code such that they can fix problems by themselves.