Google has announced on more than one occasion that the Motorola Xoom is the tablet on which they designed Honeycomb, and the tablet that will be the lead once released. In an interview with Pocketlint "Dave Burke, engineering manager for Mobile at Google and Jonathan Nattrass and Andrew Morely representing Motorola Mobility to have a talk about Android 3.0 Honeycomb." Google chose Xoom because it has the most advanced hardware of any tablet being developed.
During the development process both company's had members working together to develop of product that utilizes software and hardware in harmony and to their fullest potential. The version now being shown is the full version of Honeycomb Android 3.0 not the shell of the OS demoed at CES. Also of note is that this is a purge Google experience, showing that Google is keeping their promise to enhance the baseline UI of Android and taking that load off of the Manufacturers.
So the Xoom is the Nexus of tablets giving the pure Google experience and other manufacturers can customize their tablets as they choose to. This will be the first Honeycomb device to ship and hopefully it makes its way into the hands of reviewers soon.