I’m not a lawyer, but I offer an explanation. I may be wrong, but give my explanation some thought.
The Wikipedia article on trademarks has this clause:
Unlike patents and copyrights, which in theory are granted for one-off fixed terms, trademarks remain valid as long as the owner actively uses and defends them and maintains their registrations with the applicable jurisdiction’s trademarks office.
The key is “defends.” Now do a news search for iPhone. You’ll see a freakishly lame press release about Cisco’s new lame phone, a trademark they’ve owned for a decade. But it’s buried in articles about Apple. People have been speculating for years about Apple’s coming iPhone. Even in 2002.
And yet no word of Cisco ever telling anybody to quit referring to the product as iPhone. None.
Perhaps Apple’s logic is simple: The entire world already thinks of Apple when someone says iPhone and it’s largely due to the fact that nobody ever contested this public perception. Perhaps they intend to argue that the trademark was invalidated years ago.
P.S. For the record, my prediction wasn’t too far off.