Presumably for LAN efficiency? If you have two people on LAN using Skype it goes via LAN IP?
Also if run several clients it shows them all.
So if you keep several clients open in different places, it's at least harder to determine which IP reflects your current location, right?
That's scary if they really show the local IP. It becomes quite handy tool for hackers. If they have breached any computer in a company network and want to target the CEO's computer next they can just use Skype to get his IP.