It is the norm for all credit cards to have a series of numbers which is unique to your card and along with it a smaller series which tells you when your card will expire. Credit card companies keep track of your card use through these numbers. One would do well to ask why the card has to expire at all. The foremost reason for this is that your card has a magnetic strip behind it that wears over time with use. At some point this magnetic strip is going to be unreadable by the machines.
When a card is due to expire, the concerned card company informs the card holder. This way they maintain customer contact and in the process also discuss problems and suggestions if any. It keeps the connection between the card company and the customer going. These things go a long way in helping the companies keep their clientele as competition in this field is as stiff as in any other.
Another reason for expiration dates is the security of the card holder. There is potential for fraud in every financial industry today and credit card fraud is very prevalent. Someone might have a card issued in his name without his knowledge and it could have been running up huge bills. The need to renew a card on certain dates minimizes problems like identity theft.
Card companies are usually very keen on keeping people on as their customers and so usually one month prior to the expiration date on your card a new one comes to you free of cost. For travelers who card might expire while they are away, prior intimacy ensures the card comes to you ahead of time so you can use it wherever you are.
Once you receive your new card, be sure to read the literature that comes with it. Check for anomalies if any, contact the company for discrepancies, and wait until all the issues are sorted out before using the card. Remember that the company needs you, not the other way around. So if you want terms changed, tell them so. And tell them why. More often than not, you'll find they respond favorably.