That date is no coincidence. It's the first day of Apple's Worldwide Developers Conference, scheduled to be held in San Francisco from June 11 through June 15. (Incidentally, the agenda includes a focus on Leopard, the next generation of OS X that's supposed to be released sometime in the second quarter of 2007.)
Rumors have been swirling about the iPhone release date. One blog pointed to a release date of June 15 based on alleged documents filed with the Federal Communications Commission, but those have been shown to be a hoax.