Polygon got to talk with Lucy Bradshaw through email and she answered some real questions! The most important ones are the explanation what happened:
“A lot more people logged on than we expected,” Bradshaw explained. “More people played and played in ways we never saw in the beta.”
“What we underestimated was a huge surge in pre-orders within the last week and the power of the great word-of-mouth created by the media and our community,” Bradshaw said.
Full article worth reading: http://www.polygon.com/2013/3/9/4081464/simcity-interview-ea-maxis-lucy-bradshaw