Impossible to wiretap or monitor? The Skype client was an obfuscated blob! There's no reason to believe it wasn't trivial for Skype to wiretap individuals. After all, authentication authority was centralized. Here's a simple test: is there a password recovery feature you can do via email or so?

There may have been evil reasons for Skype's change. Or maybe, MS realised that needlessly taking customer resources to run the Skype network isn't suitable behavior?