Let me preface this with IANAL, just a very interested person.
It may very well be, but having a monopoly alone isn't not a crime. A crime in this case would be abusive practices of the monopoly.
What makes United States v. Microsoft different is a number of factors but the main factor was its restrictive licensing agreements with other OEMs. You could buy a computer from a variety of makers, but no matter what, this IE/Microsoft abusive relationship allegedly existed.
What this means is if you were an OEM, not only did you carry Windows as the operating system but that agreement forced you, the OEM, to package and include Internet Explorer. As others have pointed out at this time, downloading and installing alternative web-browsers was also a slow proposition or required someone visiting a store.
In particular it was ruled that Microsoft violated Sections 1 and 2 of the Sherman Antitrust Act
Apple does not have a monopoly over the dominant operating system for all tablets, only its own. Yes right now it is the dominant product in the space, but alternatives readily exist with the same availability as the iPad. You may argue that the Samsung case is an abuse of monopoly, I don't believe it is, abuse of IP law, perhaps - but that's a different discussion.
The way the situation would be analogous is if the majority of all tablet makers, all used iOS, and were forced by Apple to configure their installations in a way that benefited Apple products while hampering others. And even then it might not be the same, depending on how courts view the iPad as a device.