Dev/creative folks are in bullpen/open areas Marketing/sales get private offices
Justification I got a couple times was the sales people need to talk numbers, and that needs to be private. Cynically, I think they don't want anyone else (like devs) overhearing the (over)promising that's done, or hear/witness some of the desperation when things are going bad. Also, was told once that having your sales guy talk on a phone in an open office will make it sound like they're in a boiler-room situation, and lose credibility.
Fine - give everyone private/closed spaces, and give shared workspaces available to those who need it when they need it.
Still amazes me that people will pay $100k+ for 'jr-mid' level folks in some areas, but cram them in bullpens because "cost".