It all started when Bink.nu noticed that Bill Gates had a logo for Microsoft Office Ultimate 2007 in his slideshow, and then Microsoft today confirmed that there is such a version. Microsoft had this to say about the Ultimate Edition of Office 2007:
Microsoft Office Ultimate 2007 will be a new package offered in retail and OEM channels at general availability. It will give people working at home access to the full line-up of 2007 Microsoft Office applications so they can create, find, manage and share information across boundaries using the toolset they’re familiar with at the office.
I think they are creating such a version so that they have something that matches the Windows Vista Ultimate Edition title. They will probably bundle those two products together for some kind of deal or something. I doubt it was just a coincidence.