Understanding TVS diodes in this application
What makes you assume that TVS diodes don't regulate compared to Zeners?  They are avalanche devices just like "Zeners" and you can see the breakdown characteristics in the datasheet.  TVS diodes are just more rugged to handle high peak power events.

The TVS diodes shown form a crude reference for the gate of the upper cascode FET, and clamp the Vgs to a safe value respectively.

The cascode device allows the switching device to be used in an application where it is switching higher voltage that its rating, but it's not necessary to have a precise reference voltage for the gate, so a TVS works fine.