All the monopoly regulations on them expired and with Apple and Linux where they are now, you'd have a lot of trouble convincing a court MS is a monopoly. In the desktop market they are still the big dog, but Apple is a major competitor. Macs are all over the place. In the server market MS is a big player, but so is Linux. I don't know what the split is, but it wouldn't surprise me to find out Linux is on top. In the mobile arena MS is a nothing. Linux (in the form of Android) is by far the biggest with iOS coming in #2.
Thus there's no argument to be made for a monopoly position. When there's very real competition out there in all segments of your market, you aren't a monopoly. Well if you aren't a monopoly, then anti-competition laws don't apply. Companies are free to lock-in their own solution. Again for a great example see Apple, who (tried to) lock their software to their hardware and puts everything in their own controlled ecosystem.
Sorry, but the MS monopoly ship has sailed. Unless the market changes significantly, they are just another player, which means they can do this kind of thing.