Anode scanning Nixie circuit
The 75v rail is a function of the limitations of the BSX21 transistor, which has a max 80v VCEO specification. When that circuit was produced, low cost high voltage NPNs were not available. These days, you could dispense with the 75v line and use a transistor rated for >200v.

Even with 170v as the maximum strike voltage, then it would foolish to provide exactly 170v. You need to provide a voltage higher than the maximum strike voltage, and that's after voltage drops in transistors and tolerances. 200v sounds not unreasonable. 

Apart from R1 and R2, which seem to have values way too small, I don't see any current limiting in this circuit, individual cathode resistors would be the norm.