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)
As long as the company can survive, they just don't want to give the bottom-rungs much at all.
In the context of my own work as a developer, focus for me entails trying to come up with the math to do something new. This entails hours of thinking about it in bed but also trying to juggle the ideas in my head. (I'll be the first to admit that thinking is probably not my strong suit.)
BTW: I'm looking for a New Hampshire based CPA for my sole proprietorship if you know of anyone. :-)
Or the cost savings are reaped by different people than those who bear the productivity hit.
Perhaps I was too harsh, there probably are some businesses that actually don't know that developers are much different from customers support, accountants or typists when it comes to the need for sustained concentration and focus.
(I mean no disrespect to customer support, accountants or typists.)