Nothing ever said the Mayan calender ever indicated anything other than a "rolling over."
After all, it's a wheel.
On the other hand, a second hand clicks off a minute hand when it finishes a cycle, and a minute hand clicks off an hour hand when it finishes a cycle. Likewise, the Mayans say that when this calendar finishes its cycle on December 21, 2012 (winter solstice), if finishes the "Fourth Sun" and initiates the "Fifth Sun."
What does that mean?