I makes lots of sense if you think about it. There can only be one router on a network handing out IP addresses. When your router turns on it would get a IP from your service provider. Then it gives an IP to airport and all airport clients. If airport is trying to get a IP from your service provider and get a network IP for it's self and all computers on it's network. that will not work. You need to make airport get and IP from the router and also let the router give IP addresses to it's clients. Does that make sense?