Thanks for the suggestion, but I already tried that. However, in case anyone else has the same problem later and finds this thread, I did find a solution.  The problem turned out to be that I was using Dell's own software to manage the Wi-Fi adapter. The Dell software has a few settings but none related to either powering down the Wi-Fi or closing the lid.  When I switched to letting Windows manage the Wi-Fi adapter the problem went away.
On my Dell Latitude E6510 the Wi-Fi turns itself off when I close the lid, and turns itself back on when I open the lid.  I have the power management in Win7 set to DO NOTHING  when I close the lid while running on AC power, but closing the lid still shuts down the Wi-Fi. I'd rather have the wi-fit stay on with the lid closed so the laptop will stay on my home network, but I cannot find any setting to make the wi-fi stay on. Am I missing something or is this just something that the Latitude always does -- none of my earlier Dell laptops ever did this.
Wi-Fi turns itself off when lid closes, turns back on when lid opens