Remember that the production committees care as much about manga sales as they do anime sales. In
June and again in
September,
Chihayafuru was the best-selling manga in Japan. It's hard to imagine that the anime had nothing to do with this. I would not be surprised to learn that the success of the manga influenced the decision to create a second anime season.
Update:
Chihayafuru was
#16 in total 2012 manga sales.