One of my favorite business allegories goes something like this.
A manager and his CEO were talking about their training program. The manager said, “I’m concerned that if we invest in training our employees, they might find better jobs and leave our company.” When the CEO heard this his face suddenly went pale.
The manager, thinking that the CEO must not have considered that possibility, started to apologize. But the CEO interrupted him and said, “No, it’s not what you said that concerns me. Actually I was just thinking, what happens if we don’t invest in training and our employees never leave?”
I think the moral of this story applies just as much to open source volunteer communities as it does to companies.