Focused on the mobile industry, but applicable to education - Opengardens, walled gardens and mobile web 2.0: "Historically, major technology vendors have used the philosophy of “walled gardens”, often with considerable success. However, over time, we see walled gardens crumbling all around us and being replaced by Open systems and Open source. If ‘customer lock-in’ was the byword of the older players, web 2.0/mobile web 2.0 are all about relinquishing customer control."
I agree that walled gardens have a tendency of breaking down over time...though I think we see a similar breakdown in the functionality of open gardens as well. Some great ideas have come from walled garden environments...and many society-shaping influences arise from open gardens. I'm not sure this is an either/or debate. As I've stated previously, the approach selected needs to match to the outcome desired (and increasingly, needs to occur in appropriate contexts, as we are discovering with the rising influence of many different cultures and countries).