[akiselev]

Anyone is free to make their own operating system, browser, and bundle them too, yet Microsoft got pummeled by both the DoJ and EU. AFAIK (IANAL), the market dominance of a product has a strong effect on whether something can be brought under the jurisdiction of antitrust law. You're right though, as the cases I've seen mostly revolved around anti-competitive tactics, like Microsoft above and Intel for their OEM deals (both of which I think relied on their market dominance).