There really just is no such thing as a "natural" monopoly. Now, it's obviously true that many industries benefit from brand awareness, economies of scale, and other factors that make it very difficult for competitors to enter, but not impossible, and CERTAINLY not impossible if the entrenched companies did something idiotic like censoring the Internet.
This seems like semantics. An example I've used before: I'd definitely say Microsoft has the monopoly on the operating system market, considering how many people use Windows in comparison to Linux. Not that there's anything wrong with that, but to say monopolies can only exist when the government forces them to exist seems like a stretch.
This is also why I don't believe "the free market automatically makes the best product emerge via competition" logic always applies - do you seriously think every person with a computer tried both Windows and Linux and decided Windows was better? I know I didn't - I don't care that much about OS's and Windows works fine for me. Hell, just look at how many people still use IE, even though Firefox, Chrome and probably a number of other browsers are far superior.