it's not necessarily a given, the modem portion of the 400 is optional from what i understand, and the wifi radio is integrated into the LTE modem, so if one is removed the other is removed with it. the usb 2.0 and BT controllers however are part of the base soc design.
it's very likely the sd400 soc they used is a stripped down version since there is no need for a radio of any kind for android wear aside from BT, and they would want to keep the part spend as low as possible.
it could be in there though, although i would imagine with that running as well the battery would probably suffer even more
Nexus 7 32GB (2013)