This question is similar in spirit to Why do some online stores not ask for the 3-digit code on the back of my credit card?.
I don't see how asking for the credit card's expiration date as well as the number can possibly provide any extra security. As far as I know, the number and the expiration date are always given together when making online or telephone purchases by credit card, so I can't imagine any even vaguely realistic scenario in which a thief could get the number without also getting the expiration date. Unlike with the security code, you don't even need to turn the credit card around to get the expiration date, and are no rules against storing the expiration date along with the number.
If the point is just to increase the possible number of data combinations in order to prevent brute-force guessing, then it would be far more efficient to just make the number two digits longer. (Since credit cards usually expire 3-5 years after being issued, the expiration month only multiples the number of combinations by 36-60, whereas two extra digits would multiply by 100). That would also make the data format more consistent, simplify the data entry and storage.