How can you tell that your product is not just at top of the heap, but the undisputed champion? You could look at sales figures, or try to determine the installed base, but that can get tricky. It's much easier to see how your competitors behave, and whether they're going at you head-to-head, or just trying to survive on the landscape you've defined. Microsoft Office is a good example. Word, Excel, and PowerPoint are saved in proprietary formats, but Office is such a monopoly that, to have any hope of finding any customers, competitors like Apple's iWorks and OpenOffice have to save and open files in those documents, through the magic of reverse engineering. Meanwhile, you won't be able to save in Pages format from Word.
If you needed any confirmation that the iPhone is dominating the smartphone market right now, then, look no further than this interesting tidbit: the Palm Pre, not yet in public release but in the hands of various Palm employees and other testers, syncs with iTunes, downloading music both ripped from CDs and bought from the iTunes Store (as long as it's DRM free). This is the equivalent to Apple building Word doc capabilities into pages, and when confronted about it, Palm super-investor Roger McNamee called Apple a monopolist and said that people should be able to use their music as they like.
Palm appears to have pulled this off by fooling iTunes into thinking the Pre is an iPhone. Jon Johansen (aka DVD Jon, who knows a bit about breaking through DRM schemes) thinks that the Pre is sending an Apple product ID via USB to the computer it's connected to. which seems just slightly sketchy.
Apple could probably file a lawsuit against Palm for this chicanery, but there's another solution that the company might find more satisfying: just tweak iTunes to defeat the Pre's reverse engineering, then push an update out to legit iPods and iPhones that matches the iTunes update. In fact, Palm had better hope that Apple does just this before the Pre gets into the hands of customers -- because if they get used to using iTunes to sync their Pres and then suddenly find that they can't, they're going to be pissed, and probably not at Apple.