Does dual-licensing limit community?

Stephen O'Grady has an interesting post about the past, present, and future of MySQL over on Redmonk, including how its dual-license strategy may limit its community:

Generally, this model has served MySQL fairly well. By controlling the intellectual property, they retain the rights to relicense the code, thus protecting a revenue stream. They also were afforded a slightly greater protection from forks versus more collaboratively developed projects like Linux, in that they - theoretically - employed the majority of the people qualified and paid to work on the codebase at the lowest levels. But let’s come back to that.

What’s the catch to the model? In part, it’s that the burden of development is born almost entirely by the MySQL staff, but the more relevant concern here is the inability to consume external contributions - even if they’re excellent - without licensing them.

Stated more simply: as long as MySQL remains committed to the dual licensing model, it will be unable to accept the same patch set that open source only versions of the code can, because they do not share the same licensing concerns. Which is why we’ve seen these spring up, and possibly why the MySQL-derived Drizzle project has taken a different approach from its parent.

Common wisdom in the past held that MySQL's dual-license strategy was an advantage, as the company could reap the benefits of open source development, testing, and word-of-mouth marketing, while still pursuing some proprietary sales strategies.

Now that there's more value placed on community contribution and collaboration between projects, the pendulum may be swinging towards pure open source plays instead. I think O'Grady is right on the money -- the ability to consume external contributions will outweigh any benefits of the dual-license strategy that inhibits consumption of those contributions.

What do you think? Are companies that sponsor open source development better off with dual-licensing strategies that preserve proprietary opportunities, or should they be ditching the dual-license model and throw wide the gates to community contributions so long as the contributions meet their