Intel's rationale is that the dual, bi-directional 10 Gbit/s links open up possibilities for faster synching, video transfer and Express outside the PC box--things it says are not possible with the single 5 Gbits/s max USB 3.0.
three pages in this article, and still no real explanation of why TB exists. is there any evidence at all that Intel intends something more ambitious than yet another peripheral interface? I had hopes they were trying to do a sort of "IB without the pretenses". but the coverage so far makes it look like a "decommoditization" effort (against USB).