Our critters have always sent their own cards to some of our family/friends. Certainly Daddy and Mummy get cards from the kids as well as from each other -- it's interesting how their paw-writing changes depending on which human helped them.
Other than Mummy and Daddy, they send cards to those humans they feel closest to. They always sent cards to their grandparents, and they had a card for their Uncle Rupert the other week.
Neither of us admits to giving them an allowance, but they always seem to have some money to spend on gifts for us, too.
Maybe they sell the mice they catch..