While cost IS a factor, the idea seems to be going round that open plan is genuinely superior. (Although rarely so superior that the executives partake...)
Right, startup companies do open-plan because it is cheap, not because any actual developers are more productive or happier that way. It's supposed to be something you put up with until the company can afford offices... Only that point got lost somewhere along the way.
Hell why doesn't GE just remodel their offices to look like garages, because obviously that's the reason that Apple was successful...
While cost IS a factor, the idea seems to be going round that open plan is genuinely superior. (Although rarely so superior that the executives partake...)