I work at a high tech company, and of everyone I associate with there, exactly one person uses a Mac outside the office. More people use Solaris, to put that into some perspective.
Windows is irrelevant in the cutting edge sectors, yes, but it has always been. That doesn't matter. Microsoft's bread and butter isn't in the cutting edge sectors, but in established companies, and there you will find that all desktops and lots of back end run Windows, often with proprietary solutions on top built on Microsoft products (even if the actual implementation often is in a third party tool). Those places will not switch out their systems. And startup companies that grow will have to connect to other systems in other companies, such as insurance and other service providers, and will adopt Windows environments for that purpose since it's just so much easier to use what the others are already using.
Even where I work, where most develeopment and deployment is on Linux and Solaris, the business side is running on Windows with Windows products on the back end. And there is no push for, or incentive to push for, a change. Those systems will remain for decades, and guarantee income for Microsoft.
That's how things are all over. There are shims between mainfram systems and databases running on Windows, with the front end Windows software connecting to those databases. The database may in some cases get swapped out for one running on a *ix OS, but the front end remains on Windows. There are business systems entirely on a Windows stack. They're locked in, and not changing out. And lots and lots of in house business critical systems running in Excel or (if yer lucky) Access. Those are not going away, and they are usually completely undocumented and impossible to reimplement in something sane.
That's where Windows will remain relevant. No matter how much startups and personal users step away from it.