If you're going to manage a large number of servers, you probably should at least create a non-profit corporation to handle the tax aspects. "Corporation" and "open source community" are not mutually exclusive terms either: the Apache Software foundation is a non-profit corporation. Many clubs and churches have non-profits associated with them.
I suppose for some projects, a small loosely organized community can use and develop the technology. Certainly that's the impression I get of Linux in the early days. I also feel that a lot of other projects can do well with this strategy. However, when you talk about CloudStack, OpenStack, or Hadoop, you're talking about lots of servers, and lots of data. So the community has to start with larger organizations. I think it just comes down to different projects needing different strategies for development.