You actually do have to show a monopoly. A monopoly is prohibited from doing certain things that would be perfectly legitimate if a smaller competitor did it.
Example 1: The EU required Microsoft to offer a version of Windows with a browser choice screen. However, Apple does not have to offer an alternative to Safari. Reason: Windows was a monopoly, but Mac OS X wasn't.
Example 2: The EU permitted Windows Phone and Windows RT to default to IE, without offering a choice of other browsers. Reason: Windows Phone does not have a monopoly of the smartphone market, and Windows RT does not have a monopoly of the tablet market.
