This seems to be a great example of correlation does not imply causation.

Sadly I can't disprove this fallacy because I don't have a counterfactual world to show you.

But I would argue that if you look at post-DOJ Microsoft, that also happened to be the same time that:

  * Microsoft was rudderless
  * the internet became the source of lots of extremely cheap software (including SaaS),
  * Windows software quality gave us gifts like Conficker
  * Microsoft was busy prosecuting software pirates and burdoning legit users with licensing keys
  * Microsoft lost out on smart phones, tablets, cloud services, etc which grew *far* faster than desktop software
  * OS X became a more compelling alternative to Windows for home/business users
  * Linux continued to eat Windows server market share

You are blaming the DOJ (ad EU Commission) investigations for Microsoft being a massive ship and turning slowly in an age of rapid innovation. They got fat on intellectual property and patents, then never bothered to trim their business to their core competency. Perhaps this will change in the post-Balmer years, but only time will tell. I would argue that the only thing that Microsoft has really dominated recently has been console-based gaming, and it's not because MS got split up for anti-competitive behavior (because they didn't).