The retail disc edition will include all of the content from the version on Xbox Live Arcade, and it will get the same updates as the XBLA version of the game going forward. As a bonus, Microsoft is also apparently including 48 hours of Xbox Live Gold as part of the retail release.
Rumors of a release of the retail version in other regions continue, but so far Microsoft has not yet confirmed its release in any additional regions other than North America and Europe. If successful, however, we suspect that Microsoft may push it out to other regions at some point in the near future.