Cracking WEP is easy, but you would probably end up on an internal network that wouldn't get you to the Internet.
There is no techical or security issue with having multiple wifi networks in an airport as many airports have lots of them. Ideally you have one wifi network with multiple virtual access points for different companies. But increasingly the airport authority is asserting its rights and not letting airlines and others drop in their own wifi network. So the airlines end up paying the airport authority to use its network for their lounge customers. This idea will start rolling out across the world pretty soon.