It means that developers don't have to learn a new language or buy Macs to write programs for the iPhone . It means stuff that's already written can be ported.
I used to not care about Java until I recently began writing apps that ran without change on both the Blackberry and Windows Mobile devices. This opened my eyes. As one gets older you want to rewrite code less and less.
And it's quick, especially if 3D libraries are included.