The difference here is that Skype is a medium of communication outside CF. If the imms incriminate a cheater by listening in to their in-game communications, by tracking their IP address, by monitoring who they group with and how they react to things in game, that's okay.

They have no authority to pursue their CF rules enforcement outside the world of CF. That's like saying if you break the rules we'll come to you and beat you up. Or DDoS your PC. Or phone your employer and tattle to them that you're mudding from work. (Only in our case it's the investigation where they are overstepping their bounds, not the punishment.)