Brian, as you should know I never said that GPL affects the protocol. (See my previous answer to Bruce)
What I have told you is that Richard Stallmans opinion is that if you have a client/server application (both GPL) and the protocol is proprietary (ie not public), then if someone creates a new client for the server this client will also be GPL.
However, this was never an argument that I have used with MySQL; My argument has always been that if someone has an application that require MySQL and this application is distributed directly or indirectly with MySQL, then the whole is a derivated work of MySQL and thus affected by the GPL.
As a separate comment, we never had any notable problems in MySQL with getting people to agree to sign a contributor agreement for donating code to us. Talking with other companies, as long as the contributor agreement is sensible (ie, you don't loose any rights yourself), then people don't have a problem signing it. As a reference, see how many people have donated code to FSF!
The reason MySQL stopped getting contributors was that when I stopped working with the contributors (because the internal developers took up all my time), MySQL AB never assigned anyone else to do this and when the potential contributors didn't get any feedback they stopped working on MySQL.
When it comes to Drizzle, you require the code to be under BSD; In practice this is a contributor agreement too.