I am not so sure I would agree with your thoughts...but I don't really know what these guys mean with "Trusted USB Hub"
Take today's E2100 keyboard. It is a trusted device that uses the existing standards USB bus to send/receive encrypted data via the untrusted PC.
So, I am inclined to say that the "Trusted US Hub" may really be a device that allows to coordinate/execute/"do" processes and sending/receiving encrypted data to and from additional sub-TPM's (printer, sound card etc.) via the UBS bus and/or other channels...