Comment 7 for bug 1097519

The decision of which driver to load is not up to the kernel. When wl is installed it blacklists brcmsmac (and b43 and bcma). When the kernel emits the module alias for the device, which triggers the loading of the module, the blacklist causes modprobe to ignore brcmsmac (actually bcma, which would in turn cause brcmsmac to load) as a candidate for the device. The kernel uses whatever driver modprobe loads for the device.

Okay, I just found a reference stating that Ubuntu *does* automatically install Broadcom proprietary drivers if you check the "install proprietary software" checkbox when installing. The ubuntu-drivers tool is used for doing this, so I'm going to reassign the bug for consideration of whether ubuntu-drivers should cease installing bcmwl-kernel-source for wireless devices supported by brcmsmac, since brcmsmac is officially supported by Broadcom.