The movie showed a polar flip, which is different the smaller shifts. The pole has actually moved a lot in the last hundred years. Course people think a sudden flip like they showed in the movie couldn't happen, that it would take thousands of years, but if it did it's possible the polar ice caps would melt and then refreeze someplace else. That could flood a lot of the areas shown in the movie like LA and Washington D.C. COULD, doesn't mean it would. Truth is no one really knows what would happen since it last happen before recorded history.
And maybe the Mayan stuff was forced, but the 2012 date comes from the Mayans. So if that was the title from the start, then that's what they were playing off of from the start. But a lot of thought doesn't usually go into the movies made by these guys.