Their ability to do this has been known for a while - see past HN discussions:
- Https URLs posted in private Skype chats visited by Microsoft https://news.ycombinator.com/item?id=5704574
- Skype and Microsoft man-in-the-middle chats to give targeted ads https://news.ycombinator.com/item?id=7369163
People have claimed, without much evidence, that the NSA helped finance the purchase for Microsoft in exchange for making Skype easier to monitor but so far as I said nobody has solid PROOF of that, just speculation.
But I will say what Microsoft did made little logical sense. The whole point of Skype was to make running a network inexpensive and scalable, Microsoft's changes made running Skype much more expensive (and what company WANTS a product to cost more to run?).
That's the official version, anyway. You may choose to ignore reasons giving by the people who made the change, of course. The infrastructure on which Skype was built relied on most clients being PCs with decent internet connections and CPU to spare. Something that's increasingly not true in today's world.
Modern P2P designs often have measures to disable participating in aiding network routing completely for devices with limited network/processing, which effectively only leaves as much traffic/processing as messages you explicitly send/receive.
What about this piece of news from 2008? http://www.nytimes.com/2008/10/02/technology/internet/02skyp...