According to today's New York Times:
Some Dean backers see Dr. Steinberg [Dean's wife] as a role model for independent women balancing careers and children, but others in the campaign increasingly regard her absence as a potential liability for a candidate who is known for his reluctance to discuss his personal life or upbringing. Yet the topic is all but off-limits with the candidate. Voters also have begun to ask about a marriage in which the partners are so often apart — she skipped Dr. Dean's birthday-party fund-raiser, the family-oriented Renaissance Weekend, even the emotional repatriation ceremony of his brother's remains in Hawaii.It's not all that hard to understand, if you think about it. I mean, if you were married to Howard Dean, would you want to be seen in public?