There has been a bevy of credit card cancellations as of late. Credit Card issuers are canceling seldom-used cards in hopes of reducing risk. If you want to keep a certain card make sure it is used at least occasionally! (At least once per year.) If not you could find it canceled with no prior warning or you could find that your credit limit has been reduced.
http://consumerist.com/5126259/defending-access-to-your-credit-cards-lines