Fantastic article by Jem Matzan provides the background and specifics on why support for Wi-Fi in open-source, GPL, and free operating systems is so problematic: Matzan has done a superior job in tying together the technical, political, and legal reasons why it's just so darn hard for OS developers outside of major, proprietary, for-fee releases (i.e., Windows and Mac OS X) to obtain the necessary pieces to support any given Wi-Fi device. (Mac OS X is quasi-proprietary: Large parts of the system are dependent on open-source and related software, but Apple keeps many elements of its system private.)
Matzan points out that at the most minimal level, simple permission to redistribute firmware without conditions along with an OS would enable greater support with less effort. Few Wi-Fi equipment makers allow this. Further, direct access to underlying functions would also make integration simpler. Again, few companies allow this.
Going one step further, Matzan attempted to interview every major Wi-Fi adapter manufacturer, including Atheros, Broadcom, Intel, and Marvell, the big four that rewrote the Task Group N direction last year, but received no real information or response; same with Texas Instruments. Atmel, Ralink Technologies, and Realtek were enormously more forthcoming.