Another thing is that teams with private offices suffer greatly in communication and more importantly in energy and passion. Teams in open office often go to lunch together, have more personal exchanges and have far more socialization. When people see their teams working hard around them, they have little excuse not to follow the suit. In private offices, I often see people catching up on news websites and FB and in fact I even knew a guy who freely admitted that he spent entire days on YouTube. These were smart people and it's not that they were slacking off but most people are actually fairly weak against distractions generated from their own computer. Those distractions in private offices far out number distractions by people in open office.
A 3 person team packed in to a private office is likely the best of both worlds. In private offices, you mostly rely on bumping in to someone in the lobby for serendipitous discussions. Unless your work is isolated and you don't need to talk to anyone, open office is usually better option generally speaking. However I agree that people working in open office have to establish proper norms such as don't talk loud, put phones on vibrate, for long talks go outside, don't disturb a person wearing headphone etc. In most places, I see these norms are generally established.