Now the C-library is a different story. If you want to use it, then you're looking either GPL or one of their supported FOSS licenses. So, it isn't quite as bad as you're making it sound.
What really needs to happen is to have someone write an LGPL or BSD MySQL client library. That would pretty much put up a licensing firewall. This might even be the case with something like DBSlayer. It would be even more clear if the middleware supported multiple DB backends.
MySQL has always straddled this GPL/FOSS/proprietary fence, and never made it very clear if you really needed a commercial license. I could be 'misremembering', but I thought that at one time they even explicitly said that if you used Python/Perl/PHP/etc you could write proprietary software w/o a commercial license. However, they also said that if your program "required MySQL features" that you had to have a commercial license. They made all of their money off of this confusion. But I think that if a third-party BSD client library spoke the correct binary protocol to the server, that you'd be in the clear. Then again, I'm not a lawyer...