The supernodes are an orthogonal issue. If Skype is end-to-end secure then the location of the supernodes doesn't matter. And if Skype is not end-to-end secure (e.g. imagine if their CA issues MITM certs) then having supernodes in US university dorm rooms doesn't help you either.
BTW, if anybody wants a refresher, here's what Skype says their architecture is: http://www.skype.com/en/security/#encryption http://download.skype.com/share/security/2005-031%20security... It could have changed since 2005, although I've heard that really old versions of Skype can still connect to the network.