I would imagine that the reason people don't tie a husband's and a wife's address together in databases is that you might someday not live together -- you might move somewhere temporarily for a short-term job, she might want to rethink the marriage, you might need to go live nearer to your parents if they become ill, she might want to get a master's degree and get a really good offer from somewhere you'd have to quit your job to go to -- and various companies do not want you to contact them to shout "WHAT?! WTF!?" when all your mail starts going to her place or all her mail starts going to hers.

I really don't think that expecting a customer to say, "And of course I'll want both cards sent to the new address" is too unreasonable. After all, you are in a better position than the credit card people to keep track of whether or not you and your wife are living together.