There are a couple of things in what you said that raise some pretty big flags for me:
nobody gets to hidey-hole in their office, pretending to not be part of a team.
Seriously? That's what you think people are doing in their office: hiding from the team? I love being part of a good team. I love white-boarding broad design. I love sitting down and hammering out the nitty-gritty details. I even like pair programming and working one-on-one. But I am a classic introvert in that being around people is physically draining. I enjoy company and I'm good company, but it wears me out. Putting me in the same room with 5 other guys for 8 hours a day is a good way to get me burned out and exhausted with your project.
The whole business about having to waste an hour to get back into the zone after an interruption is, frankly, total BS.
This makes me seriously question the kind of work you've been doing. An hour may be on the long side, but there are lots of things I've worked on where an interruption will easily cost 15-30 minutes and have a much bigger impact on my willpower and focus. This is compounded by the fact that I'm mentally exhausted from constantly being in a room full of people.
Tracking a bug down through three layers of application, framework, and security code, for example. Writing that crypto implementation that has to be right the first time or customers get owned is another. Studying that new framework that you want the team to learn because it's the new shiny is another.
where they can go away into if they really need that occasional alone time
Look, I get that you're the boss and you get to tell me what to do. I want the team to succeed, so I'm not going to cause problems; I'll adapt to whatever you've decided we're going to do. But if you really want me at peak productivity you need to understand that alone time is my default mode, not something I need occasionally. I know I'm not the only one like this.