Not only did Microsoft miss the portable music player revolution spawned and owned by Apple’s iPod, and the smart phone revolution, now they’re missing the 64-bit revolution for Mac users. From Microsoft:
Because Apple’s frameworks require us to complete the move to Cocoa before we can build a 64-bit version, Office 2011 will be 32-bit only.
I’d settle for better compatibility between Mac and Windows versions, though Microsoft has trouble maintaining compatibility between Windows versions of Office.