From the article:

"'Protection' mechanisms added to 802.11g to ensure backwards compatibility with legacy 802.11b clients can cut the throughput by 50 percent or more."

It's referring to something entirely different from encryption. :(

So if someone isn't using encryption, it should be like 27.3Mbps...
can the widget detect that and adjust? so it's not saying 12Mbps being my max when it's probably more?

The theoretical max speed of AirPort Extreme is 54 Mbps... And that's tested in a lab setting. When in the real world, the 802.11g protocol runs into a number of issues that drastically cut its real-world performance.

This O'Reilly page gives you all the techno-babble about it...
http://www.oreillynet.com/pub/a/wireless/2003/08/08/wireless_throughput.html

As said before; great to be able to see the Mbps of my AEC and AEBS. One question. Theorectically I should be able to get speeds of upto 54 Mbps. CompactAirport shows 100% at aprox 11.5 Mbps. Is it calibrated for AE or does it calibrate itself automatically to the max speed avaible as set by the network (whatever that may be)?

This is my favorite widget! The combination of the Airport strength being in a percentage, the ability to see current Mbps rate, and the graphical design all combined together create one extraordinarily useful widget!

Plus, the designers other widgets have the same style while providing completely different types of information (processor usage info and batter info). I like the clean, professional style of the widget, and how well it looks when combined with the other two.

Great job, guys!