Even though the article's title may sound a little strange, here is some information about the way Mac OS X handles DNS:
Bolding is mine:
- You have specified two or more DNS servers in the Network preference pane (possibly at the direction of a network administrator or your ISP), but the first server on the list has become non-responsive, or was entered incorrectly. The delay occurs while Mac OS X waits for the first server to respond, then it goes to the next server in your list. Make sure the addresses are entered correctly. Changing the order of DNS addresses may improve performance. If your network administrator prefers that the primary server be used, you may wish to change back to the original order after the issue is resolved with the primary server.
Airport devices tell Mac computers the DNS servers to use, so this article applies to Airports as well.