Lisa Belkin pegs it on what it means to be a working mother. I am sure some working dads are like this*, but I am fairly positive that the rate of working moms who are like this is much higher.
*I have always been bemused by a story that a friend told me about her post-9/11 experience. She and her family lived in Tribeca. She worked a few blocks from home and her husband worked in midtown, and the kids were home with a nanny. When the planes hit the towers, she stayed at work until the towers fell, then she headed toward home to evacuate the kids. When she got there, her husband had already left work, gotten home, and evacuated with the kids. I would have done exactly what her husband did, and my husband would have stayed at work like she did.