That's no longer an accurate description of Skype. After MS bought it, it moved all the supernodes into data centers, running the nodes on MS-designed hardware, So the supernodes are effectively on an MS-owned backbone.
Erm.... no.
It is still a peer-to-peer network. The supernodes are not transit nodes, they are directory nodes.
Skype's own words:
Skype isn’t a network like a conventional phone or IM network – instead, it relies on millions of individual connections between computers and phones to keep things up and running. Some of these computers are what we call ‘supernodes’ – they act a bit like phone directories for Skype. If you want to talk to someone, and your Skype app can’t find them immediately (for example, because they’re connecting from a different location or from a different device) your computer or phone will first try to find a supernode to figure out how to reach them.
Yes they've now moved the supernodes away from clients and onto their own network, but the limited role of the supernodes is unchanged.
In Microsoft's own words (Mark Gillett, CVP, Skype Product Engineering & Operations):
"This has not changed the underlying nature of Skype’s peer-to-peer (P2P) architecture, in which supernodes simply allow users to find one another (calls do not pass through supernodes)."
For the vast majority of users, after call setup the connections are direct (and always have been).
No such thing unless you're on the same subnet, you'll always be transiting other networks and subject to the vagaries of the internet and ISP routing policies.
And again, in Skype's own words......
By using every possible resource, the P2P system that supports Skype communications is able to intelligently route encrypted calls through the most effective path possible. Skype even keeps multiple connection paths open and dynamically chooses the one best suited at the time. This has the noticeable effect of reducing latency and increasing call quality throughout the network.