Linux, *BSD, and other Unix variants have lagged in Wi-Fi support due to chip vendor's stated concerns about access to the low-level radio functions on their chips: But a meeting last month in London, the Linux Wireless Summit, apparently has helped move development along. DesktopLinux.com reports that the meeting included Linux kernel developers, and representatives from Broadcom, Devicescape, Intel, MontaVista, and Nokia. The summit is part of an effort to standardize parts of Linux for reduced maintenance and complexity, as well as greater functionality.
The summit's organizer is quoted and paraphrased as stating that the FCC will only certify Wi-Fi devices that have a closed-source component for handling low-level radio settings, such as frequency choice and power levels. I don't know that there's actual evidence as to this fact, and would love to see. That would be an extra-regulatory step for the FCC, as there is no defined required for releasing radios that cannot be modified; the onus is typically on the purchaser who modifies hardware conforming to regulatory limits, and suffering the penalties if they fail to conform.
For instance, worldwide 802.11a equipment can use the 4.9 GHz band in some countries; it's limited to public safety purposes in the US and military uses elsewhere. Using 4.9 GHz in some parts of the world could get you thrown into jail for a long, long time.
It's interesting that these considerations are now being made openly. A couple of years ago, I was provided with some of this reasoning from sources I won't identify, but told that the concerns about the FCC and other regulators couldn't be discussed publicly.
You can read some of this history in a January 2005 post that starts off discussing an Economist article criticizing Atheros and Broadcom.