Whatever definition you want to use for Workstation, in fact Yamaha have been using that description for Tyros2 &3 (and possibly Ty1 I can't remember) all the time. (ie. it's not an unofficial/cheeky invention by the current presentor )
At bottom right of the case just below where the words Tyros 2 or 3 are printed and on the front of the Manual it says Digital Workstation. If you connect the Tyros to a Computer via USb and select it in say a Sonar hardware setup menu it shows up as Digital Workstation.

John