The antitrust case against Google filed by European Union regulators on Wednesday will inevitably draw comparisons to the long-running prosecution of Microsoft, in which regulators on both sides of the Atlantic pursued the software giant for anticompetitive behavior.

But Margrethe Vestager, the European Union’s competition commissioner, may not find the comparison entirely flattering. With more than a decade of hindsight, the theories supporting the case against Microsoft have all but fallen apart, and the pursuit of the company that makes Windows may suggest a reason for skepticism about this fight against Google: The tech marketplace is fluid and unpredictable. The giants that look most unbeatable today could falter in ways that may once have seemed unthinkable — and without a lot of help from the government.

“In the Microsoft case, if they’d just waited a while, the problems they thought they saw would have disappeared because technology, consumer behavior and the market demand changed enough to correct those problems,” said Geoffrey A. Manne, executive director of the International Center for Law and Economics, a policy research organization that has received funding from technology companies including, in the past, Google. In a 2013 law review article comparing the antitrust pursuit against Google to the Microsoft case, Mr. Manne was more succinct: “Microsoft’s market position was unassailable ... until it wasn’t.”

The same, he said, could turn out to be true of Google. The rise of mobile devices and the prevalence of apps could make the traditional search engine less central. And if the regulators emerge victorious, they could end up constraining Google in a way that makes its services less useful to consumers — which would be a hollow victory indeed.