Microsoft argued it wasn't using monopoly power, because Windows was priced lower than the profit-maximizing price a monopoly would use. The Justice Department

Microsoft argued it wasn't using monopoly power, because Windows was priced lower than the profit-maximizing price a monopoly would use. The Justice Department argued that was evidence of anti-competitive behavior: Microsoft chose to deter competition with an unnaturally low price. Perhaps the argument is that Google is overpaying, and that's anti-competitive.