He is totally wrong. There are still a huge number of video, audio, and design professionals that need the power of a Mac Pro and are willing to pay for it. Why would Apple intentionally drop this market? They've had a lot of success breaking into the movie business and taking over from expensive Avid video editing workstations; there is no way they would lose this market.
The high-end market definitely needs features like PCI-express slots to connect real hardware to, 8 cores or as many as you can throw at it, and lots of internal and external storage options. Hell, a lot of those Mac Pros are connected to Fiber channel storage arrays that store terabytes of media. And he is seriously predicting that we replace all of this with a USB 3.0 connection on our iMac? Get real.