Ironically, speaking of accountants, I at least have found that in most businesses, the accounting staff do in fact have their own isolated working space. They justify it because of the "sensitivity" of their data, which is true. But the cynic in me thinks it's because they know developers tend to make more money (on average) and so they influence the situation and pitch to the CxO's to "reduce costs" by moving everyone (except themselves) into public spaces.
Your first point is correct -- it's because of the cost savings. But cost savings only applies to those critters who dwell at the bottom of the org chart.
And last but not least, significantly fewer accounts are necessary in a software company compared to the sheer amount of developers. (monkey ones or otherwise)