I loved you article about the airport system
I may have over looked it, but I believe you left out the part that if you set up multiple airports it becomes one wifi network. I set up a home with one extreme next to the modem, and 5 expresses. 2 of the expresses were in guest homes. I set them up direct feed on gigabit Ethernet. The result was from one end to the house to the other and two guest houses one wifi network. I ran a speed test and I could see the wifi bars transferring from one access point to the other but the speed test was consistent all the way through. I have hooked up other access points from other companies and they create separate networks.