I think media definitely has played a role. But, like all things, there is some truth to it and the degree to which moms 'argue' varies greatly. In fact, I don't think moms are really arguing with one another. Instead, I think women are struggling to come to terms with their choices and decisions, and seeing what others have and other choices people have made breeds some jealously and/or resentment, even in the best of people.
As a mom who works part-time, I see multiple perspectives. I think some working moms see moms who stay at home and wished they had more time with their kids or simply to do things for themselves. Likewise, moms who stay at home see moms who work and wish they had some more 'adult time' or that their jobs as moms were more valued by society.
But, I think there are increasingly "shades of grey" as more women are working, often in nontraditional, flexible, part-time jobs, and that people's situations often evolve as their children age.
I think it's natural to some degree to compare yourself to others. The problem comes in when others judge, resent, or disrespect others. It goes in all directions. And, I think as women struggle through parenting and their choices as mothers, wives, and friends, usually people learn that people's decisions, and parenting choices, are more complex and multi-faceted than they originally believed.