The PC grew up and Microsoft along with us did too, so how can we now say it’s a monopoly?
It is a practical monopoly, just like that of Intel. Economically you have little choice besides Microsoft on an Intel-based PC. Any other choice takes extra time and effort because they are not Wintel. To qoute Depeche Mode:
"It's a competitive world,
Everything counts in large amounts".
Suppose you lead a company. Virtually everyone you hire uses Windows at home. Sysadmins for non-Windows (N)OS'es are few and your present IT-force is likely Wintel trained. So what are you going to do? Wintel. Sure, there are exceptions and their small numbers
prove the rule.
Again, it is not Microsoft's fault or even original intention. Far into the 80's computermanufacturers were fighting it out with their own systems. One eventually had to prevail. That turned out to be Microsoft.
How can we say it is a monopoly? Because it is in practice, it does not matter if Microsoft intended it that way. It is everywhere with little competition. The only competition of any kind survives because it needs no marketshare to exist. That is the strength