You bring up a good point. Right now, we're still small so everyone has a support day and talks to users almost daily. At this size, we all appreciate the close communication with the people using our product and we write those cards out of free will (not just a job description). Chris wrote more about it here:

http://particletree.com/notebook/the-4-12-day-workweek/

Now, as the company grows, this may have to be adjusted. The cards did not start as some marketing stunt, and we never want that message to be sent to our users. When cards from developer X don't feel personal enough, we'll have to brainstorm some more creative ways to thank our users.

His self-description was not completely accurate. Chris Campbell is a co-founder of Wufoo.