That is a REALLY interesting question.
There is no reverb in the Aux send either. This is a note from Hilmar-at-Bose about why that is so.
Q: Why is there no Reverb on the Aux output of the T1 ToneMatch® Audio Engine?
A: Hilmar-at-Bose writes
The T1 ToneMatch® Audio Engine has lots of different effects units and normally they are unique to each channel. That means that the T1™ has 4 individual dynamic processors, 4 modulators (chorus flanger, phaser, etc.) , 4 EQs, 4 delay processors, etc. The only exception is the reverb, which is shared by all channels.
The AUX is also a per-channel control. That means if you turn up the AUX of channel, you expect to hear signals from channel 1 and only from channel 1. However, the output of the reverb processor contains the reverb portions of all 4 channels. If we add that to the Aux, you'd hear the reverb portions of all 4 channels and not only the channel that you are interested in. In most cases, this is probably not what you want.
If you are familiar with conventional mixing consoles, you will find that the situation is quite similar. You can only route to an AUX output effects that are specific to a channel (normally these would be connected to the insert loop of this channel). The "shared" effects typically come into the board through an AUX return, which is not channel specific.
Source: No Reverb on Aux
The reasoning seems equally applicable with respect to the USB - at least since you can assign individual channels to the USB output.
Maybe we can get some more insight from someone-at-Bose.