“Our work to increase compatibility means we haven’t completed the transition of moving the entire user interface over to Cocoa yet. “In Office 2011, we’ve made investments in better compatibility between Office for Mac and Windows Office, which is the largest request we receive from customers,” MacBU product unit manger Jake Hoelter said. The reasoning behind sticking with 32-bit support, according to the company, is because they’re still working on transitioning to Cocoa for Mac OS X.
Microsoft’s Office for Mac 2011 is scheduled for release this fall, but it won’t include 64-bit support.